I understand entirely and don't listen to the flaming - I'm sure you feel bad enough already without these people putting the boot in too.
I would try to rehome the second cat then see how you get on. It will probably be a huge relief. You gave it a home when it was abandoned. You have done a good thing - taking on a second cat is always difficult anyway.
I would contact a local rescue and ask them if they could put it on their waiting list.
We took on a cat about 10 years ago when ds1 was small. She was in need of rehoming as her owners had got another and they didn't get on. So we had her.
Last year I wasn't coping well with the house as I was pregnant, then had a new baby and was left on my own with 3 children - it was a mess, we had to replace our back door so could no longer have a cat flap. There was nowhere to put a tray, it was awful trying to keep up with it, and she wasn't happy, and she ended up being outside much of the time, sleeping in a cosy old pushchair with a cover on it - I felt so cruel but it was that or random accidents in the house and I felt like we just could not cope.
In short I rang up the sanctuary near to us and spoke to them - they agreed she would be happier with them, and a few months later a place became available and off she went.
It was awful but it was basically her or the baby. I had to keep telling myself she is a cat, she isn't attached to me as such, and we gave her a pretty good life for 9-10 years.
She is 15 now, apparently very happy, I do miss her and sometimes want to go and get her back. But it would be wrong because she would not be happy here, and though I feel like such a failure, I think it is the best thing. Obviously had I know the pregnancy and so on would be so difficult, and that I'd be alone during it, I wouldn't have done it. A lot of things suffered including the other children.
But what's done is done, we had a stark choice to make. I feel awful still, but when you are in between a rock and hard place sometimes something has to give.
I fostered many cats for another rescue years ago, am very fond of them in general, and used to judge anyone who couldn't look after their pet for its lifetime. Now I can see there are sometimes good reasons. 