With the contorted quince, I wouldn't chop the crossing trunk. Quince styling works unlike styling for any other tree. Quince have a culture all their own, and crossing trunks can play an interesting part in developing your tree. What I suggest is that you let them grow for for at least a couple of years, and then see where you are. In the meantime, get all the information you can on these interesting plants. Peter Adams book The Art of Flowering Bonsai has a lot of good information on quince. Colin Lewis also has good info in The Bonsai Survival Manual. The thing is, you can let your quince go, and not feed them, and water them as infrequently as you want, and they may still flower and grow because quince are really tough. But to get the most out of the tree, and to learn and grow yourself, these trees have to be taken care of, fed and tended to. If you do this, quince will reward you with explosive blooming and a long lasting flowering season. It's a two-way proposition.