Regarding the poly dating bit, I can understand how it might be difficult to find someone compatible, but it's not an insurmountable problem. After all, I'm poly, bi, I have children, and I used to date an Aspie. That both he and I were highly geared towards precision in our communication was definitely a bonus, as was a shared interest in linguistics (although I never could quite share his enthusiasm for trains
). What I'm saying is, since I exist it stands to reason that other women in your area who would be compatible also exist. Everyone has things about themselves that might make it more difficult to find willing partners; it's more your attitude towards those things that predicts whether you'll be successful or not. Finding one who would also be interested in S and G would be more complicated, but still possible.
What concerns me more is how the communication between the three of you has broken down, and how it seems from your description that your needs are being ignored. The lack of condom usage, when it's clear that you expected condoms to be used, is an example. I can understand a dislike for condoms, but there are ways to work around that. Is it the latex or the spermicide causing the sensitivity? Have other brands been tried? Even something as simple as taking a Benadryl beforehand can alleviate some of the problems. Now, it's a bit moot, as she's already pregnant.
You've been incredibly supportive in this situation, and from an outside perspective, it does seem that they've taken this as an opportunity to walk all over you. At the very least, I think a long conversation with all three of you present and participating is in order. Your needs are just as important as theirs are, and yours are not being met in the current arrangement.