Can my son and I as freelancer make user account on the same PC
No and never because it is against fiverr TOS
If you and your son have separate accounts and are selling different services then I don’t think its an issue.
That shouldn’t break any rules in theory, nothing in the TOS about only using one computer per account - just one account per person. However, it may not be the safest thing to do, because it can be hard to tell on the other side. However, Fiverr asks for ID verification now, so if you are clearly two different people, different connected PayPal accounts, etc. it should be fine. Ask CS.
try to understand fiverr Terms https://www.fiverr.com/terms_of_service?source=footer
hope it help you