Yes, URI are very contagious, and it is probably going around and around. The asthma is probably not helping little Mollie. Does your vet think an xray is in order for Mollie's case? Unfortunalty I do not have enough knowledge about FIP to be of much help. Even the people at the vet's office say that is a very difficult disease. They could carry it for months or years and have no effect. ^ years ago I lost a 12 years old cat to FIP, at least that was the diagnosis at the time. But I had her for those 12 years of her life, and how could she have had it. None of my others ever seemed to get sick after her and until this month I haven't even thought about it again except i have a sick cat and am wondering myself if this disease isn't coming back to haunt me. But for URI, I do belive they last a week or 2 so maybe the asthma just makes it worse for her.
Keep us posted.