Hi!
If you buy specifically for multiplayer, forget Port Royale 2; that has no MP capabilities. However, PR1 does.
1.)Port Royale is somewhat difficult, but not hair-pulling-annoying difficult. If you go through the tutorial and spend some time to consult the manual (both before playig the game and when you encounter something new while playing the game), you'll not have much problem.
It IS complex, what with all those cities, products, manufactures, but one can get used to it. This game is definitely worth the effort of learning to play it.
2.)Although I've never played it in MP, from what I've heard, there is some interaction between human players, but not much. You play as one character, and your brother plays as an other one. You both have your own ships, buildings and all, and go after your own business. However, you can co-operate, for example, by deciding who produces what in a given city, or by one of you attacking a pirate hideout and the other finishing it off, etc.