Should I stay or should I go now?

IMHO the living take precedence over the dead. But I would also arrange for flowers or some alternative to be sent to teh exMILs funeral.

You can’t do anything for the mother in law, I go with spend time with the aunt.

i agree with what @WestRiverrat and @poisonedantidote have said

If you go, will there be trouble?

More importantly: if you stay, will it be double?

Sorry, it had to be done

I wouldn’t give up the time you have left with your aunt.

Go to your aunt.

Ex-MIL comes with ex-spouse who possibly has a new life? If you are close to your ex-inlaws, and your ex-FIL is still alive, fix a casserole, drop it off at the house on the way out of town. Explain that you have a family emergency, but didn’t want to pass on paying your respects.

Aunt, absolutely.

Aunt

Aunt. And send flowers for the funeral.

Aunt, aunt, aunt. Send condolences to the funeral.

See the aunt for sure.
and
sorry you have to choose