I am sorry for your loss.
This link may be of assistance to you:
Please note there is no simple or easy solution that provides you the full value of your father's collection as well as a timely clearance of same. But if you have the time, eBay is most likely your best solution for value in the long haul for at least the oldest of your father's collection (1920's and older).
Also, there is a "dealers directory" link in the upper left margin of the main page.
After you've read my guide (for a better idea of the value of your collection), you may wish to contact some of dealers for reference, or perhaps a business arrangement of some kind.
Remember, they have a bottom line they must satisfy, i.e. they're in the business to make money.