can you join both factions? cause im doing the mages guild right now and i want to know when i beat the mages guild can i go directly to the telvanni?

Sure, no problem. There will be a slight disposition loss but nothing important. I join both with almost all my characters.

k cool i was planing on joining both and then i might join the temple

The only limit is that you can only join one Great House. Other than that, you can join anything you want. Some of the guilds have conflicts but there is always a way around them.