goodness you do have your hands full! has you wife's therapist been successful at all about her agoraphobia? if not, i'd consider another T for her. i suffer from that too but not to any extent as her. seeing a therapist helped me learn tools to deal with the feelings of being scared to leave the house. since she's extreme with this i hope this suggestion is feasible. the longer she stays in the house the more difficult it is for her to leave it. i know. at one time it would take a crowbar to get me out.
as for your thinking abou the past part of that i believe is romancing a time when you weren't so burdened. when see your therapist do you vent all this? perhaps this is something you can discuss with him/her. ..and your stress too.
you've got a lot of pans in the fire. the wife's sister and kids, your wife, etc. i hope things improve for you. use your therapist a lot to untangle some of these issues. i do believe things can work out for you.