Yeah, i knew it would be difficult!
I've though about swapping the sides of the cage they are in, but R&R don't like being picked up (they had bad handling experiences for the first 1-2years of their life before we got them, and are still difficult to get - getting better, and happy once you've got them!!) and the other side of the cage has no access apart from at the top (wasn't a problem with Ben and Jerry - they come to you). I am concerned about being able to get Rum and Raisin out when it comes to cleaning, but i'll give it a go! I've swapped part of their bedding over so they get used to each others smells, and all of their toys. they are now sharing a sand bath too.
Generally they get introduced in the cage, as there are few places in our house that are neutral and degu proof. the only place we really have is the bathroom and when we tried that last time, it resulted in dismantling the whole bathroom to get under the bath because raisin squeezed through a tiny gap down the side of it!!!
They are always making chattering noises at each other and following each other around the cage (jerry is always following R&R seeing what they are doing), which always makes me think its a good sign, but then this is followed by nice play fighting and sniffing and a little bit of attempted grooming, then the louder chattering (usually started by Jerry), and tail flapping. there is some bottom nipping too and then it all goes wrong and they end up in a heap wrestling and covered in saw dust.
I think secretly Jerry really wants to go and play, but he wants to be boss and is going to be really stubborn about it! I'm hoping he'll realise eventually that if he wants to play, he has to play nice, or he goes back to being on his own!
thanks loads for the suggestions