Should I close a joint credit card account?

The current advice given by financial experts is to keep open credit lines you aren't using. These days, having a lot of "open end" lines of credit (like credit cards, home equity loans and personal lines of credit) is helpful to keep your utilization ratio low. The utilization ratio is the total amount you owe on revolving credit divided by the total amount you could possibly borrow. You want that number to be 30% or less. So the more you "could" borrow, the better.
Do you have enough credit cards in your own name only? Was this card issued to your mom and you co-signed for it? Or was it issued to you and your mom co-signed? Are you just an authorized user of a card issued only to her?
Being an authorized user of a card isn't as important to your credit rating as having a card issued to you based on your own credit. If you are only an authorized user, I am not sure you should still be using the cards. Technically, authorized users have no responsibility to pay the balance due. The person to whom the card was issued is the only one they can sue for payment. I think using credit cards that were issued to a person who is deceased might be considered fraud.

Interesting. Just why would you keep those accounts? Just curious. I know you said emergencies but having extra credit cards just opens you to more fraud.

This is what I have been told. Each of those credit cards have a credit limit. Lets say that you have 4 with credit limits of 10k each. If you go to the bank for a loan they consider that 40k that you can chalk up debt. They do not care that you pay them off monthly. You have the ability to rack up 40k in debt.

I see no reason to have more than two major credit cards going. Use one for gas the other for everything else. I do have a couple of store CC's because these are my two favorite stores and I get huge discounts with them.

Do you want to close them? I would notify them that mom has passed and you are sole owner of these accounts now and wish that they remain open but no more cards in moms name. Unless you have terrible credit I am sure they would like to keep you as a customer. If not, open a no annual charge CC in your own name and keep it for emergency.