Let's turn to each member of the in-law triangle:
Luke says nothing but disappears to his workplace when his mother visits. Luke, you are crucial to improving the in-law tensions. Reassure Mindy that she is your top priority, above children, work, mother, and money. Mindy will hopefully respond with a similar declaration. After clearing the air with your wife, have a discussion with your mother. Thank her for her visits and gifts. Inform her of your children's clothing sizes and respectfully explain that you'd appreciate gifts that fit them now. Ask her to please refrain from unsolicited advice, reassuring her that you will not hesitate to ask when you need anything. And in the future, don't make yourself scarce when Mother visits; make sure to notify both mother and wife when you are unavailable. Your Mother comes to visit you, too.
Mindy: it's tough raising 2 pre-schoolers while pregnant with a third, especially when your husband works long hours. Your need for physical assistance and emotional support is understandable. Perhaps you can obtain additional parenting information and guidance from community resources, or one of the many parenting books on shelves today. On the other hand, criticism from your mother-in-law is an issue your husband should handle. Ask him to speak to his Mom about your complaints. She will not be offended by his criticism; a mother forgives almost anything her son says.
Finally to Ms. Mother-in-law: you're an accomplished woman. Just as you mastered law to become a lawyer --quite a feat after a divorce - you must master new rules to be a parent-in-law. The primary rule is to refrain from unsolicited advice. Instead, ask your daughter-in-law what you can do to assist her most. Second, be aware that constant criticism hurts more than a physical injury. Try to empathize with your inexperienced daughter-in-law. It is her turn to make mistakes with her life and her children just as you did. Talk to your son, instead of your daughter-in-law, about critical matters. He will forgive and forget what you say while your daughter-in-law won't.