If your dad wasn't a collector, but just "saved coins" he came across that were old, foreign or otherwise unusual, then it's highly likely that none of the individual coins are scarce or rare. Rare coins are valuable because there aren't many of them, and coins selected at random aren't likely to be one of those rare ones.
Coins are also valuable if they are in good condition; again, if your dad wasn't a collector and wasn't paying money for high-grade examples, then it's highly likely that your coins are going to be in low-to-average condition.
I'm not saying "your coins are no good", I'm saying it's best to set realistic expectations. That way, any rare or above-average coins will be an unexpected bonus. Your dad might have just happened to obtain some amazing coins, by accident - but it's not highly likely.
So let's talk minimum possible value. The pre-1965 silver coins will actually be made of silver. If the coins aren't rare or high grade, then their minimum value is whatever their silver content is worth - which is considerably more than face value these days. Right now, if you add up the face value of all your actual-silver coins and multiply that number by 15.33, that's the value of the silver content.
For pennies and nickels, their minimum value is face value; any value above face they might have is entirely in any collector premium, so date, mintmark and condition will determine the value.
For foreign coins, your best bet is to look up the NGC world coin database
. This will at least give you a ballpark idea on whether a coin might be valuable or not. If you can't ID the coin, post pics in our ID Required subforum and we'll help ID it for you.
As for "how to sell", you've basically got three options.
1. Take it to a coin dealer's shop, and sell it for whatever the dealer offers to give you. This is the quickest and easiest way, if you need the money in a hurry (eg. if you need to settle the estate quickly). But it will likely result in the lowest price you receive for the coins.
2. Sell it by auction. Coin auction houses generally are only interested in valuable coins and have a minimum value for accepted consignments. Auctions tend to get higher prices, but you need to wait until the auction is held - which might be several months after you submit the coins.
3. Sell online, by eBay or other online venues. This is likely to get you the highest return, since you're selling direct to collectors, but is slow (since you're selling coins one at a time) and you have to put in all the work getting them up on eBay, then all the work packing, mailing, dealing with troublesome buyers, etc. There are also special rules you need to comply with when selling coins on eBay. I'd really only recommend this path if you or someone else in the family is already confident an established at selling things on eBay.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis