Thank you everyone! That's really helpful to know I've done the right thing separating them, I wasn't sure if I'd been too hasty but thought it was rather safe than sorry! Especially given I have no real idea where they've come from - they were definitely a Pets at Home purchase so who knows if they were even from the same litter. I feel much safer leaving them when I'm out of the house knowing they can't hurt each other anyway!
I'm excited to start with their taming sessions, I've started with the tissue trick just now and am making sure to go over and chat to them when they're up and about, just trying to get them a bit more used to me gradually. I get the feeling their last owner didn't really take much to do with them while they were there sadly, but I love a good challenge so I'm sure I'll get them there with some patience and effort
Thank you so much for the link as well souffle, I'll be sure to have a read!