Wow, what an incredible honor and task! Can you give us some photos of some coins, obverse and reverse? Are any of the coins graded by a third party grading service IE: NGC,PCGS, ANACS, etc, are they just loose, in albums, coin capsules, slabs? gold, Silver, platinum, CuNi?
I would start by separating by type and face value. A daunting task, but you will need to take good close up cropped photos of every coin. Safely store those images on a thumb drive. Make sure you have adequate insurance coverage on the collection. May be guess at first. Keep the collection in a safe. If you don’t have one, get one. You could obtain a professional ANA certified appraisal done by a licensed professional. At least try to list them in a spreadsheet for a list. I catalogued over 80,000 baseball cards for my son last year. It took me six months, but Excel had no problem with that number of lines.
good luck. Look up American Numismatic Association professionals and you might want to even hire an attorney to help you with the valuation and appraisal. My wife and I discussed this very issue a month or so ago, and it got us both thinking about it, however I don’t own but a dozen albums and around a hundred graded coins and several hundred loose coins in flips, slabs, and capsules.