God, this is the most difficult situation I've read about for ages. I can't see how anybody can judge you for WHATEVER decision you make, even a tiny bit!
Basically, the hard truth is that this is going to HURT whatever you do. I know you know this and typing on MN is an outlet for some of it. We just need to listen and give you an outlet.
People who have said have the baby and then have it adopted - this would hurt hurt hurt! She would never get over it! The child would be deeply affected by it too! It is SO not an easy option (I know you weren't saying it was really, but I want to stress how painful this would be - (sore point for me))
People who think "every child is a blessing" - this is way too simple. What if she has the baby but is too knackered and psychologically messed up to bring it up properly, so the child lives a troubled life and the mother lives with the guilt? What if all her other children suffer as she no longer has the mental and physical resources to be a good mother to them? Then she suffers from the guilt of that as well? Deciding to terminate would not be selfish in any way, it would be selfLESS, for the good of the unborn baby and her existing children. This decision will ALSO be agony for her and her DP but she would be protecting the feelings/welfare of all the children not just thinking about her own feelings.
Having to make this decision is so terrible because two instincts fight each other - the instinct to have your unborn baby and the instinct to protect your existing family from anything which might not be good for them and to do the best for them.
And even if she did just think of her own feelings it's hard to see how anyone could blame her when every decision would be so painful for her personally. This would be completely natural.
The best thing would be if there were ways that could be put into place which would make her feel she could definitely cope with this baby and all her other children and do a good job of it and keep her mental health. Could this be possible? Isn't it incredibly incredibly hard? People who have been through it - how possible/likely is this? What are the practical ways of coping?
It makes me feel faint to imagine having to cope with all she has to do AND a newborn, and the possibility of her losing her mind.
And if she terminates - the pain and loss and grief of that! The effect of that on her mental health could also impact on the rest of the family.
It's a case of finding the least painful option for the least number of people out of a bunch of options that are ALL going to be painful.
LB, I really feel for you and I do agree with the people who said see a counsellor/therapist to help you get through this, whatever you decide to do, because I just can't see how anyone could cope with this alone! You said talking would just make you cry but crying is good! You need to cry, a lot! How can you get over it if you don't express it? I know you have to stay strong for the rest of the family but repressing all of it will make it worse long term won't it?