If by Marneus you mean Marneus Augustus Calgar, then he is not the Primarch of the Ultramarines. That would be Roboute Guilliman, while Marneus is the current Chapter Master of the Ultramarines. And Erik Morkai is a Wolf Lord who leads one of the 12 Great Companies of the Chapter. Logar Grimnar is the Great Wolf, AKA the Chapter Master while their Primarch is Leman Russ.

What chapter does the Space Marine belong to? And what weapons does he wield.

Shit about to go hell in handbag. Good chapter tho.