To use the same Windows licence key on 3 different machines is strictly illegal.
As the vast number of Win 11 Pro models are mostly sold to business clients, the likelihood of either OEM or Retail is practically zero.
As the vendor of the licenses is not disclosed your only chance to avoid Microsoft locking your account(s) and machine(s) is to contact Microsoft and get them to check the keys prior to upgrading.
Bear in mind, you are not big business to Microsoft, so don’t expect too much in the way of courtesy.
BTW, if these keys are so-called generic keys installation will be no problem. Snag is that after 30? days you’ll be made aware that you need to licence Win 11.
I fear, even PayPal will not reimburse in case of money lost.