Without a Social Security or ITIN number an individual, in most all cases, cannot be on the tax return.

It is the starting point for everything, impossible to e-file a return that is missing one and an immediate rejection if it does not match the Social Security Administration records

You are correct about the parental dependency deduction, but you need to review the qualifications to be eligible to take the deductions. Why are they filing a Joint return, unless it's just to get over withheld taxes back. Are they checking the box that says they are being claimed as dependents by someone else? Does your client pay all the bills or do the parent's contribute?