If you are close to them, I would go to the parties and not stay very long. There's no harm in attending and you can mingle w/the guests w/o having to interact w/your wife. If she can't handle your presence there, that's on her, but both your FIL and MIL are close to you and would love for you to attend.
BTW, your wife won't issue an invitation because she's not the hostess of either party, she's a guest, just as you would be. If you think you are strong enough to attend, I say go for a while and then make your excuses and leave early.
Just my two cents.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
