Banshee will be quietly wary about the newcomers, although given how his usual demeanor is, it won't be too much of a difference. Experiences with alien species back home have not been the best, and he might have a few flashbacks because the Fallen back home also have four arms, but at least so far that's all the Thessyx have in common with them. He's aware that all of them are technically the ones who are strangers here, and so long as there's no hostility he otherwise won't have any problems with them, although he'll wonder why the 'children of the Leviathan' are the ones getting priority attention.

...and then he'll forget about it.