Thankyou for responding!
I actually just cleaned out the cage yesterday, but it's the same stuff i've been using since i got them.
I just tried putting Marley in beside Cid in the smaller cage, and they were fine together. Cid went straight up to him and they sat together and started grooming each other. Then i took Vasquez out the big cage, he is very skittish. Since we first got them, Cid was the adventurous and friendly one, he loves sitting on your shoulder and hiding in your hair. Marley and Vasquez took a little longer to get used to my boyfriend and I, but Marley is just as friendly as Cid is now, and Vasquez will jump on your hand and come out, but after a little while he gets really fast and doesn't seem to want to be handled.
Anyway, when I put Vasquez in beside the other two, they immediately started to fight again, it was so fast I couldn't tell which one went for Cid, but they started the squeaking and running again, and Cid ran to the door and as soon as I opened it he was climbing up my arm. I put him back into the big cage, and he seems glad to be back in the spacious cage. I'm thinking about just putting Marley in beside him since they seemed fine together for the 15 minutes or so, and leave Vasquez in the smaller one but I have it right against the big one so they can still see, hear and smell one another.
Vasquez has always seemed greedy. For example if he's at one of the food bowls, and another one approaches, he'll move around the bowl and turn his back to the other so they can't get to it. This isn't all the time though, he just seems to have his grumpy days.
I'll give it a few days, and maybe alternate Marley between the two of them since he seems to be neutral.
The degus do get plenty of attention from us, so I don't think they'll get too lonely. After a few days i'll try introducing them again and if it doesn't work, then i'll see about getting another friend for Cid as neutering any of them is a last resort for me.