How can I have two nodes of different content types update to each other? I have two different content types(A &amp; B), and I want to be able to have a field in content type A that is a select list of all the nodes from content type B, and then I want to have a field in content type B that is a select list of all the nodes from content type A. 
Is there a way that I can have those two fields update each other?

Ex: in node 'Atest' from content type A in the select list field I select the 'Btest' node from content type B, and then if I edit 'Btest' in it's select list field I can see 'Atest' already selected. (showing that 'Atest' has it selected)

Is that possible? if so, what would be the beat way to go about setting that relationship up?
You can try Corresponding node references.

I used this to sync up Events and Venues on one of my sites, and whenever I switch a venue for an event it automatically changes the node reference on the other node, so I only have to change the node reference once, instead of twice. Keeps things tidy, works with multiple.