M.S.
We know 4 families that moved here from SF. Two of them started here, moved to SF for 10-20yrs, then moved back.
One family lives here because of the sense of community they never found in SF. Even though they have family out in SF, they have more help and 'extended family' here (something you said you don't have), as well as other benefits that you mentioned.
You really have a tough decision to make! I know that moving to be with my dying father made a huge impact in my life and I'm so glad it worked out for me, so I can understand wanting to be with your mom.
Good luck!!!!!!