Can 2 blocks have the same previous hash? Can two blocks have the same Previous hash after being created.

2 blocks totally different from each other but with the same previous hash
Can two blocks have the same Previous hash after being created.


Yes, two otherwise valid blocks could be created that both link to the same parent block, but importantly: only one of those two blocks will become a part of the valid chain. So ultimately, only one of them will be valid, and the winner will be the block that miners build on top of first (and thus it becomes a part of the longer chain). 

The other block will become what is called an 'orphan block' (though some people prefer the more exact term, 'extinct block'). 

You can look through the orhpaned-blocks tag for more info.