I own lemmings tribes, and there is a big 2 on its cover.
Here
While Oh No more Lemmings is a stand alone game, it is considered as AddOn for the first Lemmings. It features 100 new Levels and some new tilesets, but its more or less the same as the original Lemmings.
Lemmings 2: Tribes has lots of new Features, like Ninja Lemmings and i think there is even an astronaut Lemming.