Can anyone take out more than 1 balance transfer card?

Bad Idea. Whenever you apply for the second balance transfer card, a hard inquiry will be added to your credit report, and reduce your credit score.
Your friend may easily transfer different credit card balances into that one balance transfer card.

Why does your friend need another balance transfer credit card? Don't underestimate the credit card companies. They know that your friend is sitting on a pile of debt. They may not agree to give a card to him. Secondly, the moment he will apply for the second balance transfer credit card, it will trigger a hard inquiry and that will hurt credit score.

It is better not to take out another balance transfer card. Ask your friend to make repay the debt within the time. Otherwise, your friend may fall into credit card debt soon.

I think it's better for your friend to opt for professional help if he's not able to repay the credit card balance on his own. If required, he can opt for debt settlement to get rid of credit card debt by paying less than the outstanding amount at the moment.
You can settle on your own or take help of a settlement company.