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.
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.