Sharing my unpublished thesis with other students?
Of course you should share your thesis: the purpose of doing research is to increase and spread knowledge, not to keep it secret.


  Is it common to keep your thesis between you and your advisor - and potential researchers who may want to work with you?


No, it's not, and I suggest you to ask your advisor what he thinks of such an idea.


  And now he wants to do research also and try and join a research group, etc.


Well, this is a good thing, isn't it?