I just want to apologise for giving you the wrong advise by suggesting a bonding bath as I didn't realise it shouldn't be done with cross gender bondings. This is what I was once advised to do by someone and it worked for me but I do hope you didn't do the bonding bath and this is what's made things worse. I feel bad now
I am sorry that things have taken a turn for the worse and I am also sorry that Cas is poorly. I didn't realise that but it is great you have taken him in and took him away from whatever situation he was in.
I can't advise on whether you should try again with Sweep and the girls but please try and not feel bad if you do need to return the girls although I know it is difficult and I know exactly how you feel.
I had a failed bonding a few years ago when one of my sows wouldn't accept a neutered boar. He ended up in a right state from where a fight had broken out and I have never felt so guilty 1) for what happened to him and 2) because I had to return him.
But at the time, I did what I thought was right. I had no space for a spare hutch and I already had 3 girls who I didn't want to split. But I had to do what was right for my girls and the boar.
Riki (the boar) ended up going to a new fantastic home and he happily lived out his days with a wife in a lovely indoor home. His new owner was and still is a facebook friend.
All decent rescues would prefer for any piggies who do not work out to be returned to them so please do not worry as Gogi and Elder will find another nice home and I am sure the rescue would let you know when they are re homed if that's what you wanted.
xxxxx