For son at 12 years old, my advice is different than for adult kids. Ask son what he’d like to do. A card? Flowers? A plant? A gift? A meal? (For even younger kids, less asking and more just doing with them.)
Then help son get the Mother’s Day acknowledgment/gift. Depending on what it is, you may or may not need to participate.
Just make it about supporting your young son giving his Mom a gift is all.
I understand the nervousness about the lawyer meeting. Getting some a knowns in the current sea of uncertain will help.
D
Feelings are fleeting. Be better, not bitter. Love the person, forgive the sin.