In addition to recommendations above, there are folks who make a living buying and selling old kit collections. You probably won't get a lot per kit, but it will save you the hassle of doing the inventory and pricing and everything involved with selling.
If you are good with selling yourself, and have time, that's great, too, but if you need to get the collection out of the way so you can deal with the rest of the estate, this is an option.
You'll have to get a hard copy of the Finescale magazine and look up the listings of these businesses in the back of the mag. Depending on what genre most of the kits are, listings in Finescale are probably better for a varied collection, but you may want to look up the similar listings in the back of a magazine like Scale Auto if the collection is mostly scale cars.