I am only going to address one aspect of your post, and that is having your DS pay rent. And I'm not going to chime in as to whether it is appropriate or not; only you can decide that. In my experience, my DD split her time between my XAH and myself during her final year of High school, and she received Social Security benefits for a few months as my XAH is on disability. Prior to her 18th B-day, the money went into his account, but after she turned 18 in February, it went directly to her. This impacted XAH's income significantly, and he demanded that DD start paying rent...to both of us. Saying that I needed to back him up. So, my solution was to charge her rent (we all agreed to 10%, which was about $60 to each parent.) This only lasted until she graduated in May, which amounted to 4 months rent. When she went to University in August, I simply gave it back to her in full, as an allowance. I am a bit more financially able to do that, so XAH had no reason to question it. I don't even know if DD told him about the allowance afterward. Anyway, your SO may consider such a suggestion, as he probably understands that DS does have needs that extend beyond his own childrens'.