A small detail I noticed:

During and after the immediate aftermath of the assassination attempt, Michael at first shield's Kay's body with his own to protect her from being hit. After he asks her, worried, if she's hit, holds her and reassures her softly "it's over, it's over." In that moment, you get a final glimpse of the Michael we meet at the beginning of the first film - a last moment of human vulnerability. I have to think this was something intentional.

Ever since Michael greeted her at the schoolyard in 1951, their relationship as depicted is very cold, and only becomes chillier as time goes on. Michael is her husband; her owner; he is the Boss not only of his Family, but also of her and their family. They are but extensions of him. She is his wife.

Her questioning annoys him (where at one time, he voluntarily told family secrets to her, almost half amused and half embarrassed by them). They are a modern couple in 1945 at the wedding; partners. After he comes back, they are, at least Michael wants them to be, an old fashioned Sicilian man and wife.

But in this brief, brief moment of softness during and after the assassination attempt, he's Mike. For perhaps the very last time.

Michael was warm and loving to Kay in '45, but when he came back from Sicily and reconnected with her in New Hampshire in '47 (wearing that ridiculous homburg hat and looking like a pint-sized banker), he might have been negotiating a merger or acquisition with a weaker company--in fact, he wanted to own Kay (listen to the bloodless way he said, "I love you"--it's a wonder she didn't keel over from fright).

His actions during the Tahoe shooting were instinctual (good, protective instinct) but that scene wasn't about warmth--it was about survival. Kay certainly didn't take it that way--after the shooting, when she was clutching Mary, she gives him a look that would kill. It was all over between them at that point.

Why do you point their meetup to '47? GF seems to make plain that he met her at the schoolyard in 1951 ("That was seven years ago" she says of his promise to have the family be legit, in 1958).

But yes, the whole meeting is very almost creepy. It is totally a business arrangement to him. It's like he acquired her because life dictated he needed heirs and thus needed a wife, and she was the easiest to obtain since they had previous history - nothing more. I think whatever humanity lived in Michael (and he was always cold, as we see in the flashback to 1941) died in Sicily.

The timeline discontinuities in the Trilogy can be maddening. In GF, Vito's birthdate on his tombstone is April 29, 1887 but in the flashback at the end of II, it's December 7 (probably 1890 or 1891 to judge from the first scene in II, which is in 1900). In a deleted scene in II, when young Vito meets young Roth, Vito looks to be about 29 or 30, but Roth is a teenager--about 17 or 18. But, in the Havana scene, set in 1958, his birthday cake says, "Happy 67th Birthday," giving him a birth year of 1891, about the same year as Vito's birth.
Yes, Kay said "seven years ago" in 1958, which would put the New Hampshire scene i 1951. But, that was in II. In the actual scene in GF, we see a '47 Ford Woody station wagon as the two walk, and Michael's limo is a '47 Cadillac.
I put together a timeline based on the novel that I believe proves that Michael couldn't have been in Sicily very long--certainly not until 1950 or '51:
http://www.gangsterbb.net/threads/ubbthreads.php?ubb=showflat&Number=580389&Searchpage=1&Main=20650&Words=%2BMichael+%2Bin+%2BSicily&Search=true#Post580389

Well Said. Mikes reaction directly after getting shot at was much more a survival instinct than warmth. I also loved that you brought up Kay shooting him a dirty look when holding Mary. You can tell this was pretty much the final straw for her. Even when they were dancing before the shooting she didn’t look too thrilled that the baby will most likely be a boy. At this point she knows the family is t going legit anytime soon and that Mike desperately wants a boy to take his place one day. It’s hinted at that Mike knows Anthony isn’t interested or a fit for that job which is why he wants another boy

That's a very good point, JC. Why else would Michael fixate on a boy? And, why would Kay, when informing him about her abortion, shout out "It was a boy, Michael!...and I had it killed because this Sicilian thing must stop!." I think Kay not only knew "legitimacy" was impossible, she also knew she her only role in her marriage was to breed another Don.

I think you are being too harsh!
Whilst the women's primary role seemingly was to produce a heir and a spare! - I wouldn't say that was Kay's "only role" in their marriage

Did Michael really love Kay?
Michael and Kay, when they were dancing at Anthony's party, seemed quite loving They spoke lovingly and proudly about the baby feeling like a boy

There was indeed fixation on boys

As regards Anthony -
Where?

I always thought the Sicilian "thing" sounded forced, unnatural, or whatever. Why didn't they just say what the thing is?

As I'm sure most here recall, Coppola and the surviving stars did a panel at the Tribeca Film Festival a couple of years ago. During that discussion, Coppola revealed that the abortion angle was Talia Shire's idea (around 1:10:00 here):

https://youtu.be/Xd71uVNlbLs

That it's an outsider's insertion to the script may explain some of the questions it raises, like, "Who the heck is going to abort Michael Corleone's child?" But it also explains why you then work your way backward through the script to find Michael dancing and asking Kay if it's a boy; and then freaking out at Tom over whether the miscarried child is a boy. They're just building an emotional ladder that Kay can eventually pull out from under Michael, whether it's plausible or not.

. Agreed. Plus it’s unclear if Kay knew about Appolonia or not at this point. If she did then it supports that theory even more in her mind

I reckon she looked thrilled that the baby will most likely be a boy, proudly stating the baby feeling like a boy
They already had a boy so killing the unborn 'son' is not going to stop anything and nowhere It’s hinted at that Mike knows Anthony isn’t interested or a fit for that job Where?

As per their conversation, Anthony had taken his place, wanting to help Michael as of now not wait for someday

"legitimacy" was difficult not impossible
As we most recently debated in Did Roth sort of win? thread he had achieved the semblance of legitimacy and as We see in GFIII more "legitimate" than ever

She wants the unholy and evil Sicilian thing to stop by being unholy and evil herself, killing an innocent unborn child to spite her husband and the child's father Nice!

She was a prisoner couldn't even go to the market
If medical check ups "Who the heck is going to abort Michael Corleone's child?"
It is implausible Pete but no doubt made an emotional ladder that still gets pulled out from under all of us

Did anyone else notice that .......

Success?

As implausibility goes and as far-fetched as is [what will we debate! otherwise] among others -

• Who killed the bedroom assassins – can stretch to Fredo
• Why tell Fredo “Hyman Roth will never see the New Year”?
• "Who the heck is going to abort Michael Corleone's child"?
• Kay was a virtual prisoner at the Tahoe estate while Michael was away yet Michael never questioned the abortion?

She had it killed by who what proof

He killed all the heads of the other families and was the only one left standing Then became “legitimate”
You believed that story? You believed that!