The heady days of bitcoin mining are over. People mined all the easy ones early when nobody else was doing it. It gets harder and harder to factor the increasingly large numbers necessary to mine a new bitcoin. Now, there are more and more people mining bitcoins using ever more sophisticated hardware setups (we're talking server farm style setups with 100's of GPUs doing all the hard computation.)

Unless your father-in-law invented some new computer chip way more efficient (like more than 10x) I doubt you'll even make your $5k back. Or even the cost of the electricity to run the thing for that matter. On the other hand, if he has really invented something that will push forward computational technology that much, the bitcoin mining will be chump change compared to the award money and honorariums he's bound to receive for his discovery.

http://bitcoin.stackexchange.com/questions/13161/how-long-does-it-usually-take-to-mine-a-bitcoin-block

My advice would be to pass on the bitcoin mining. I'd be very interested in your experience if you do decide to go for it though.