I've got thoughts on this from two angles.

1) My sibling is divorced and I am very close with the ex's family. One of the sisters is one of my best friends and we talk regularly. I invited them all to my wedding. My sibling has no problem with this. There is a boundary - I don't discuss my siblings private business with them (and vice versa) and while I am cordial with the ex, my relationship is with the extended family.

2) My SO is VERY close with his ex's family. I don't have a problem with this. Certainly I think my SO would support his ex's family in such a time - we have actually done this together. They are very kind people and have often invited me to participate in activities with them. However, this is me, SO, and SKs, not with the ex there as well unless it is a holiday or special event (not just a dinner or something). He routinely communicates with them and does social activities with some of the family members without me - but the ex is never there. The purpose of this is to maintain SO's relationship with them, not his relationship with the ex.

I replied to one of your other posts, and I'm not trying to use the history to draw too many conclusions, but it sounds like BM in your case isn't ready to let go of having your SO as her partner and still treats him like a husband. BM calling him to gossip and report on his own family is weird. It's one thing if he communicates with her to let her know that something has happened to someone she cares about, but IMO, BM shouldn't be contacting him so much or making food for you guys, or sending pictures. That's HIS family, he can get it directly from the proverbial horse's mouth.