Can I back out a tenure track faculty offer? Summary: Signed a contract with school A while waiting for decisions from school B. Now got offer from B, and want to back out of the signed contract with A

What is the best strategy to back out a tenure track faculty offer and minimize its negative impact on both sides?
I am in an awkward situation. I interviewed two schools, A &amp; B, this spring. School A made me an offer while B is still in the interview process. I contacted the B's committee chair about A's offer, the committee chair just said, everything is slow, no way to control it.
I asked around for suggestions. I was suggested by many people to take A's offer just to secure a faculty position. Yes, I did. After I signed A's offer and got ready to start this August, B suddenly notified me and is gonna make an offer.
B is a big top university and is very close to my family. A is a small teaching university and is very far away from my spouse. I visited A and their faculties are very nice. The chair is very supportive.
What should I do? I feel very guilty if I tell A, say - sorry, I cannot join you now.
Should I ask B to defer the starting date for 1 academic year, so that I can fulfill my duty at school A for my first year's contract so that A will not get mad at me? What shall I do if B will not agree to defer a year? Just back out A's offer brutally?
Any comments and suggestions are welcome and appreciated here.
Thank you!
There's no way to do this gracefully. You call school A and tell them that you will not be joining them after all. Afterwards you deal with the fallout.
Before doing so you may want to estimate exactly how bad the fallout will be and whether it might affect your ability to do your job at school B.