A curious feature of Paradise Lost is that Milton refers to all the fallen angels by the names they'll have later on as false gods -- because that's the idea, right, all false gods are fallen angels and that's why they have some power, it comes from the real god, who is God. Presumably Satan, whose current name is the Hebrew for "adversary" (and therefore also his job description), loses his original name and starts being called Satan as soon as the war in Heaven begins, but it's not clear what Beelzebub and Nisroc and Belial and those guys are being called right now, hundreds or thousands of years before those names will be coined. And we're only hearing this story because Raphael is telling it to Adam and Eve, so is he using the false-god names, and if so doesn't that mean that God already knows Adam and Eve are going to eat the fruit and produce offspring who thousands of years in the future will come up with the names Beelzebub and Nisroc and Belial? And if that's true, doesn't it mean that the Fall is preordained, and therefore that God is full of it when he says Adam and Eve have free will and are strong enough not to fall? (Actually, he says that Adam is strong enough not to fall; Eve has no strength because Milton has a very low opinion of women.) The whole thing's a theological quagmire. Even more so because this is when we learn that if God lets them, the two angel armies will keep fighting literally forever because they're so evenly matched; this has all been an elaborate setup to make Jesus look good by sending him to clean house after the hill fight. So he gets in his sentient sapphire chariot pulled by cherubs, or cheriot, if you will, and shoves the rebels out of a hole in the side of Heaven. And the rebels fall for nine days and Milton doesn't explain why their wings don't work, but I guess you don't need to explain things like that when one of your characters is omnipotent.
The more I draw Beelzebub the more I like him. Satan rebels because he is prideful and wants power, and presumably that's part of the motivation for all of them, but Beelzebub seems to be motivated mainly by his love for his BFF Satan. Raphael, which is to say Milton, doesn't specify that he stays by Satan's side during the war, but I imagine he would. He's Satan's lieutenant, after all. You can't just leave your commander sitting on a gun all by himself.