hi guys, need some advice on the matter below,

I got a vita while my cousin got a PS3, can we like share the same PSN ID and subscribe to PS+, and both of us will got the benefits of PS+ right? I mean mine on vita, his on PS3. Is it ok to do like that? And I realised that i can create a sub account, so does this means i can also make my cousin's email under my sub account and while he use it in PS3, he will get the PS+ benefits too? Thanks!