I'm not gonna lie, it's a pretty weird series. Earthbound is the American name for the 2nd game in the series, the one most people have played. Mother 3 was never released over here, but there's roms and a fan made translation, so it's totally playable and totally awesome. I've never played the first one, I've heard that it's charming, but super hard and tedious.
Actually, it's pretty impossible to get a legal copy of either game, since Earthbound is totally unavailable outside of the rare ebay appearance, for crazy prices. You have to go for the somewhat sketchy rom and snes emulator route if you want to play. ZSNES is a good emulator, but rom sites can be pretty nasty, so here's a copy that I uploaded to my own serverright here! Yay, virus free.