“If you look as Neri's face when Mike gives him the order about Fredo on the boathouse, he's upset.
I think despite everything else he likes Fredo and at the funeral scene, when Mike is " forgiving" Fredo, Mike looks up at Neri and Neri has a very somber look on his face and gives a very subtle nod. Almost as if so say ' I don't want to do this, but, I have to do this”

So true It broke Michael's heart too And left a chain of broken hearts
“I killed....I ordered the death of my brother. He injured me. I killed my mother’s son. I killed my father's son”

“Also when Fredo first walks into the funeral scene, he walks up to Neri and says " Hi, Al."
it looks like Neri says something to him, but it's edited out, Neri has a look like, Sorry you came Fredo”

If my memory serves me right,
Neri gives a stricken look knowing Fredo's time was up [sorry Mama died] but I don't seem to recall Neri saying anything to Fredo? Definitely warrants another look at that scene!

“Neri then walks up to the casket and I take it as him apologizing to Momma for having to whack Fredo”

This is very astute observation Something new to look for, at next watch!

Rocco could have camouflaged his gun, say, perhaps in his pocket and even shot Roth through the pocket or something considering Rocco was so close to Roth? Anything but the way Roth's killing was done!

And thanks Guiseppe Petri