You see my problem here is that there are a lot of claims, some of them legit, some of them looks legit, but they're just not true. And they're mixed without separation.The AI will look at a couple of factors when deciding whether it wants to join the coalition, true; but if Charlie inheriting his brother's lands and taking pagan Saxony gets Irish tribals, the Slavic feudals in the Balkans, Muslim Africa, and the Magyars upset enough to join a coalition due to the infamy gained despite Charlie not having made any move in their general direction these factors cannot have a meaningful impact as it stands right now.
Question "should everybody who is in range (by the way, didn't see it with Africa) be afraid a kingdom that just expanded essentially twice and taken northern neighbor" is legit, and intresting enough. It can (and should) be discussed.
But question "In CK2 all you have is one value (infamy) for one character" is just simple - no they don't.
Also they aren't upset, that can be easily seen by their relations. And by no means coalition OBLIGE it's members to enter war. I'm not sure there is even a prestige hit for "regretfully not coming to your wars".
Maybe Pope don't want some great muslim empire in Holy Land and on the opposite side of Mediterranean Sea from him, who really can use ships? Hmm, it's impossible to understand. Silly silly pope.Declare holy war for Oman. Even the pope jumped in against me.