In this auction league, you don't have a rule that stipulates that bids cannot put a team over the allotted cap?
Most auction leagues have this rule.
Also, part of the cap is not touchable to ensure that you can pick up all 17 players. For example, if the Cap is $100, with $1 min. bids... then $17 is held to the side. You can basically only bid with $83.
This ensures that you fill the entire roster within your cap.
Now, rules are rules... so if these rules aren't in place... the other owners may just be abusing the loopholes. If they are breaking the rules, there should be immediate penalties (severe).