I'll take Chip's lead as an excuse to post an update
I renamed Snoopy to Mauser, however I can see why he was named Snoopy (he's a real snoop - even after the initial introductory phase). He's still
a little congested and sneezy from the upper respiratory infection, but is much
better than he was. I just moved and he seems to be much
more comfortable here than he was at the last place. I don't know if it's just timing (he did seem to be getting along better in the days before the move), if it's the place, if it's because the new place doesn't smell like a dog and 2 other cats that he can't find (which is probable), or the noise level (he gets startled by sudden noises and this place has a lot more background noise to drown out small sounds), but he is noticeably calmer and more comfortable. He and Sid have also finally gotten used to each other. I had let Mauser out of isolation (from being sick) in late December or early January, so it's been a couple months.
Amazingly, Sid never got too upset about Mauser's presence; he never tried to stalk or attack Mauser and never really objected to him. I did try to make the introductions slowly, letting them see and sniff through the cracked-open door and such, but when I let Mauser out Sid would just sit and watch him with wide-open eyes that seemed to suggest that he wanted to be friends. Sid would hiss and swat at him if he came too close, but otherwise not a peep. They proceeded like that for a while and eventually seemed to settle into rather separate lives, although they would conspire to kill me every time they wanted to eat.
Since being here, however, they have both been hanging out on my bed, usually at least 6-10 inches apart but facing each other. During the move I sat their carriers facing each other and that actually seemed to help Mauser a bit (Sid's been through too many moves to care). A couple days ago I started hearing squawks and yelps from Mauser and was afraid they weren't getting along, but then just last night I was in the kitchen and Mauser started grooming Sid - breakthrough! Since then I've been seeing them start to play together - the squawks resulting from grooming that turns to biting. They can also now both curl up with me at the same time, which could never happen before.
Sid also seems much happier, so I once again seem to have a happy family
Now I just need to finish getting fully unpacked so that they will have places to hang out other than the bed, and I will have a happy home to go with the family.