I agree with axeman, in that I never like to veto a deal.
In our league, all trades are open to discussion. If 2 managers object, the trade is put to a vote and majority rules. In my league, with 7 managers asking to veto, we would not allow the trade.
We have had a few lopsided trades where a few managers voiced their displeasure and we had a vote. I argued heavily that the trade was terrible, but should be allowed because both managers thought they were doing what's best for their team. I think the most vetos we recieved was 3 or 4 out of 11, so they passed.
As some persepective, the one guy who we thought was getting jobbed ended up winning the league last year, while the other guy seems to have a stacked team on paper, but has never pushed past 3rd. So you never know. You have to put personal biases aside and play the game.
The fact that they are brothers and this is a money league makes it difficult. I think you do what Axeman suggested and get each of them to state their case as to why they are making this trade and why it will better their team. If Team A can't give you a reasonable response, you have to veto.
12 Team H2H Yahoo Dynasty League
G, A, +/-, PIM, PPP, GWG, FOW, HITS -- W, GAA, SV%, SO
3C - Backstrom, Stepan, Roy, Krejci, Bozak
3LW - Neal, Hall, Ladd, JVR
3RW - Horton, Callahan, Pominville, St. Louis, Atkinson
4D - Doughty, Phaneuf, Faulk, Campbell, Schultz
2G - Ward, Dubnyk
Farm - Anders Lindback, Mikhail Grigorenko, Joe Colborne, Charlie Coyle, Jakob Silfverberg, Matt Hackett