Raising my son to believe in Santa, but family ruining it! Help?

So I have a son who is 2 and I really want to raise him believing in Santa, but his aunt says it's "lying" to your children so she told her kids that Santa is not real and they are saying it around my son. =/ It's going to ruin the fun for him. What should I do? I loved believing in Santa as a kid it really made the Christmas season even better. Giving my son the happiest and fun memories are what's going to matter and I think Santa brings more excitement so I don't know what I can tell him when he's a little bigger and his cousins are telling him Santa isn't real? What should I do?