Writing this on your profile to minimize spoilers. The armoured guy and the collasal guy are friends. They were in the training with eren, the two guys are never shown apart. The guy who wanted just to stay in town was also in their training group, he is the guy who hates eren, but after finding his friend's (marco) corpse, he changed his mind and wanted to join the scouting legion. The guy who didn't save eren's mom was just a soldier who was a friend of the family, no-one important as of yet.