I'm hoping they keep 5 RB's.
Ridley in the same capacity as last season handling the primary ball carrier responsibilities.
Vereen in an expanded role this season, taking on the role that Woodhead handled last season as 3rd down RB and scat RB. I also hope to see him used in the passing game in a capacity similar to Hernandez where we move him around to isolate particular match ups.
Blount is somewhat of an unknown for me, based on his size and skill set I'm hopeful he can take on a role similar to Sammy Morris. Which would be as a power RB and used as change of pace, along with goal line and short yardage situations. I'm also hopeful he can contribute occasionally in a FB capacity.
Washington is a player I see here primarily for special teams and used as our KR and maybe our PR as well. I can envision them attempting to get him the ball in space on the offensive side of the ball but no more than a handful of times per game.
Bolden is a player I view as the only RB capable of being a primary ball carrier if Ridley went down. I think he could as a 53 man roster player who is unlikely to dress unless Ridley is out for a game, or he could fits on the game day roster because of his ability to contribute as a core special teams player.
Based on how Washington and Blount add significant value in special teams I do feel the roster could justify having all 5 on it. Just my thoughts; I'm not an expert on RB depth by any stretch of the imagination however so don't go adding them to your fantasy teams.