I'd imagine that as he hasn't handed in a signed contract, that he's not obliged. However, he did accept by email, so I'm not sure.

If I was him, I'd accept one of the other jobs, assuming they have an earlier start, pay etc is good. Then let the other company know that as they have mucked him around, he can no longer work for them. Without a signed contract, notice is 2 weeks.

GL - they sound disorganised/dodgy