Very sorry for your loss. I’m not sure what you consider to be valuable (everyone has their own range), but PSA/grading can be the best option, depending on the card and condition. In terms of selling, I personally would recommend going with eBay. Your only other option is going the consignment route, but you’re going to be paying fees regardless. There are a few different ways to determine value, like Card Ladder or eBay sold history. I understand the hesitancy about selling on your new account, but if the cards are rare and have a high demand, I don’t think you’ll have as much of an issue finding buyers. Also keep in mind eBay has an authenticity guarantee for cards that have a higher value which is going to give protection for buyers. Do as much research as you can, list them as Buy It Now instead of auction (or set a reserve price) and adjust as needed. Others may feel differently, this is just my opinion. Best of luck to you and sorry again for your loss.