1) Yes the ownership is or will be, of course, contested.  So they cannot sell them until that is settled.
2) He probably had to turn over the keys in order to contest the ownership and/or to cut a deal.  In any case AFAWK the FBI does control the two addresses.
3) They will not sell them until everything (ownership, guilt, etc.) is all settled and appealed.
4) When they sell them they will not use any exchange, they will auction them off just like they do all other seized assets (gold, cars, boats, houses) through their already established methods and protocols.
5) I expect that they want the most USD they can get (not the least) - as this all goes directly into their budgets.
6) These people are not stupid and (for the most part) they do follow the law or their own internal regulations.  We are not talking about the CIA or NSA here.
7) They do not give a shit as to what Bitcoin is, whither a currency, asset, "digital gold" or whatever.  That is not their job.  They just want the most USD they can get to line their budgets.

I could be wrong.  I would be willing to bet on this but the event (sale of the BTC) is so many years in the future that placing a bet is not very practical.  I wish I could in order to just shut up the hundreds of threads on this same subject every day, day after day.  It gets very tedious.

I guess I could bet "The FBI will not sell or otherwise dispose of the DPR coins in the next year"  but who would be stupid enough to take the opposite side on this bet?