I definitely think that the new character with Sherry Birkin is Steve Burnside but that a last Wesker child is also appearing as there seem to be hints in the trailer.
First, in defense of Steve, there is the comment of his blood being valuable, something Wesker has already stated in his report in the past. Second, his focus on money seems to be a call back to his attitude in CV where he was always looking for personal gain. Finally, and most important imo, if you pause the trailer at 2:30, you can see the man's hand as green and reptile-like, very similar to Steve's mutated transformation in CV. I think its important to note that Darkside Chronicles had Steve revert back to his human body when killed which could signify that he survived but his transformation back to his human body was incomplete. I think it also fits with the theme well of both Birkin and Steve being notable infected individuals of the series.
I think the girl with the new guy has been confirmed to be Sherry Birkin but the new guy is still a mystery. Anyone not think the green reptilian left hand he uses to inject himself with in the trailer hints toward the character being steve though?