Mame has lots of great multiplayer games. As an example, we've been playing Trog and Gain Ground lately as a family. Bubble Bobble is another obvious choice, b

Mame has lots of great multiplayer games. As an example, we've been playing Trog and Gain Ground lately as a family. Bubble Bobble is another obvious choice, but really there are thousands of 2-4 player coop games. You can usually set the difficulty directly in the arcade machine setup, or by proxy by limiting yourselves to a certain number of coins. A warning that unlimited coins can just make a game a never-ending grind because you don't have that failure/reflection loop to skill up between attempts and you can end up way beyond your ability to succeed by just feeding coins in.