Yes you can play together. First, you get more than one character so why not play more than one race? This way you can run with them while deciding which is the most fun to play. If that still happens to be opposing races then consider changing alignment so they can live together. Turn your demon into an angel, or your beast into an abomination. Turn everyone neutral and live on syndesia but go home when required, you'll be able to collect resources from 3 planets where otherwise you'll be more limited. Some things will be easier if you're the same race, but if willing to work to be together it could be very rewarding to be different ones.