Elycium is right - to a point. What it depends on is who did what work on the costumes. If your two friends are not making any part of their costumes, or providing a part of their costume to be judged, and are merely warm bodies in your performance, then overall you may still slide under the Novice umbrella. But if they're contributing ANYTHING that will be judged - even revisions on the skit script, music for the performance, a wig that they intend to get workmanship judged - then yes, you have to enter at the level of the most qualified person in the group. If that person is a Master, then you're entering at Master.
But, then comes the caveat: not all masquerades are run or judged the same way, so your best bet is to run it by the director or cosplay coordinator. Whoever's in charge at THAT con. Be honest and up front about just how much work is coming from each member of the group - and if the two masters really are contributing zero, then make sure you say so. Then the director can determine, according to their rules and their judging system, whether you should be in Novice or Master or split the difference. It may be that they allow you to be judged separately (for workmanship) in a different class.
In such a case, it's definitely a good idea to run it past the director of the masquerade regardless - because if anyone recognizes the other two and knows they've competed at Master level before, and they hear your skit announced at Novice, they may be confused at best and accuse someone of cheating at the worst. As long as the director has had final say and cleared you for which division to enter, they can handle any confusion that arises later by saying "we said so, period." And you're all safe. So that's the general guideline, but definitely ask the director.
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com