This message was originally posted by
Mike.
I don't know but I'll offer some thoughts. We had a 13 yr old foster son whose care giver was bipolar. The lithium treatments made it so that she couldn't remember and even denied conversations, even to us. This left things very unsettled. Also a condition of her illness is that she was overly possessive of him, even though she was the step great grandmother. She alienated the rest of the family and us in efforts to keep him to herself.
Some of the research I did on this included a very good book, "The Unquiet Mind." It is written by a psychologist who suffers from this disorder. She said that it is possible to successfully raise children when there is another person to take up the slack during her phases. With both potentially in deep depression, I wouldn't think that this would be a good idea.
Nonetheless, your will is strong and your intentions pure. Maybe you could do respite foster care to give other foster parents a break on some weekends. If you are both not doing well, the respite can be rescheduled.
Perhaps there are other ways to volunteer to help chjildren, a community center or church, etc.
Since it is the in-laws' home, tehy would have to be licensed in our state.