a) He cannot "move here" for three months. He can enter the US on a VWP up to 90 day but cannot work. No try-outs, nothing!
b) He can apply for jobs and hope to find an emnployer willing to sponsor an employment based visa. Entry deadline April 1, kind of a lottery, if visa is granted he can start work in October.
c) You can mary him which is the least troublesome solution.
d) He can try the investor route.
e) To work within the US he needs a visa. There is no visa for "remote work". Employers are unfortunately not always up to date in visa issues. The monkey is on the employee's back should there be problems.