If you do decide to forgo hiring your father in law as your GC, what is your plan for finding, evaluating and managing an "investor friendly" GC from afar?
Getting multiple bids is best practice--from what I read, the concern here really seems to be based on rehab cost. Which to me seems to be a bit unfounded at this point. You have a wealth of knowledge available with just a phone call.
Run an exercise: Find a property that fits your buy criteria (could be currently available property or a recently completed fix and flip*), send him the pictures plus SOW and ask him what he would actually bid for that work. Use that number for your underwriting to see if it would still allow you to hit your objectives. If yes, you have your answer. If it's far off, you now have a breakdown in hand to share with him why it wouldnt work.
*A recently completed fix and flip would work best for the exercise as you would likely be able to source purchase and sale price, plus before and after pictures.