Chris Penrose

I'm not sure where else to post this but I'm having a problem having my friends play on my server. With one of them on and me (2 in total) I play fine but he has a some lag that's annoying. Then when we have a third person join the lag makes it impossible for them to play at all. We all checked our internet and that doesn't seem to be the problem. I also have made a tekkit lite server and we were able to play on that with out a problem. Anybody have an idea for the problem or a way I can fix it?