Jack liked Terry Sanford (considered him for the VP slot in 1964 as a matter of fact), though I'm not sure he liked him yet. But, I think he's the strongest possibilities.
On Bobby, the Kennedy's were as ambitious as any other powerful American family (The Rockefellers, the Bushs -you wouldn't believe how ambitious the Bushs actually were which would compare to anything the Kennedy's could muster-, etc.) but not that ambitious. Bobby needs experience first.
Civil Rights would likely still pass in the 1960's, but it could run into some stronger Congressional opposition than it did (there were a lot of pro-Civil Rights folks in Congress who could twist an arm too, though maybe not as much as Johnson).
Butterflies from there depend on whether Jack lives or not following November, 1963.