I was wondering If i could help the gangs like, The kings and the Van Graffs and still keep my alliance with NCR?

With the Kings at least, yes, you can. Save your favor though if you want them to forge an alliance later.

Don't know about the Van Graffs

I need more information on this topic.

The Kings, strangely, are one of the most fleshed out parts of the game. There are a lot of different ways to complete their quests. Depending on how you choose to complete them, you could end up gaining or losing NCR rep.

Keeping the peace between the Kings and NCR requires more work, though. You'll need to do the optional parts of the quests, such as talking to Julie Farkas. Later on in the main quest, the NCR will send you back to them, and if you haven't used your favor you can resolve their problem quickly. Otherwise, you'll have to choose the right dialog options and DO NOT attack Pacer no matter what he does, or the Kings will become hostile to you.