Hi, welcome to the forums!!!
Quote: "Is everything we create with DB Pro etc commercially our own, ie. ours to sell?"
That depends, if you have purchased DBPro then yes you may sell your games commercially and the copyright is yours (so long as your multimedia is yours aswell, be careful when using other people's multimedia). The free version is for non-commercial use.
Quote: "And are we able to create massively multiplayer games?"
Theoreticaly, it is possible but projects this big are generally recommended for teams and generally aren't attempted by one person.
Quote: "Also, because I have only just stumbled across this site and DB Pro, can you guide me to some top examples of what can be done with DB Pro, I'm only interested in 2D.
"
DBPro (I'm not sure about the free version), comes with examples which demonstrate some of DBPro's power. You can aslo check out the program announcemnts board to see more of what DBPro can do.
Hope this clears everything up
A clever person solves a problem, a wise person avoids it - Albert Einstein