I would give up B. Marshal (or B. Edwards) and J. Jones for P. Thomas and T.J. Housh.
Keeper League (3 players, 1 per position) 1QB,2RB,2WR,1TE,K,DST 6 pts for any TD, 1 pt = 20 pass yrds, 1 pt = 10 yrds run/rec., .5 pts/rec. QB: Romo, Sanchez RB: Turner, Benson, J. Jones, Harrison WR: B. Marshall, Wayne, Edwards, N. Washington TE: V. Davis, G. Olsen K: Akers D/ST: Minn
I would make the trade if you can do it for edwards and jones. Edwards and Housh are basically equal and Pierre Thomas when healthy is an upgrade over Jones. I wouldn't do it for Marshall though. When he is not acting like an idiot (which it seems both he and the coach are back on good terms) he is one of the top 10 receivers in football if not top 5.
I would definitely make the trade with Bralyon in there. I would not do it with Marshall not because it would not be an even trade but because it downgrades you at WR (Marshall --> Housch) and doesn't really help much at RB as your already have two starters in Benson and Turner. Not sure you will want to start Thomas over either of those guys. Might depend a bit on matchup.
I'd make it without question if you can deal Edwards and J Jones for Thomas and TJH. Really, you would probably be getting two better players...Edwards may be a hot commodity right now because of his surprising big game on MNF, but you still are not sure what you're getting. TJH is at least solid, and he would probably be on your bench anyway behind Marshall and Wayne.
Obviously getting Thomas would be great, and you would have the opportunity to shop for a trade since you'd have 3 very good RBs.
I think I agree with others that I wouldn't want to do the trade if you have to give up Marshall. WE all know he has the potential to be a #1 guy, and everything I hear about him is very positive coming out of Denver. Obviously he has his downside since he is a knucklehead and what not, but I'd want to hang onto him, since you don't really NEED to do this trade since you already have two good RBs.
Bottom line, with Marshall in the trade it slightly decreases your starting lineup. With Edwards, you are not touching your starting lineup but adding some great depth at RB with Thomas, and not hurting your WR depth.