True Turnbull same as Michael killing all the other Family Heads

My two cents worth!
Tess and Clem already had their own separate operation
So I reckon, they would just rebrand as their own "family" and continue as before, independent but a la Michael/Clemenza/Tessio

I was under the impression, any Sonny's business was absorbed into their operation and there was no other business out of the Corleones for them to split it in half, or fight each other for sole possession

We'd discussed in Vito's vs Michael's caporegime thread Barzini can't afford “to wait until Vito died [not knowing when?!]
The longer Barzini waited as Tattaglia said at the Commission meeting “as time goes by and his [Vito's] position becomes stronger....

As regards Nevada gambling, I reckon it was Barzini who thought he already had a toehold in Vegas through Moe Greene's hotel with whom he'd already made a deal