Is it safe to take Tylenol with codeine and oxycodone together?

If you were prescribed codeine by two different doctors, then you should ask a pharmacist or one of the doctors first before taking both of them. If the second doctor that prescribed the codeine to you doesn't know you're already taking it, then him prescribing it to you was an error. Taking two types of codeine together is effectively taking a larger dose. Taking too large of a dose of powerful drugs like codeine is dangerous.

On the other hand, if a single doctor prescribed both to you, and told you to take both of them, then you probably should.