PAOK is owned by a Cyprus-based holdings company (DIMERA) whose titular head is indeed his son; at least, last I checked. That does not have much to do with ownership, as a shareholder that owns a controlling percentage of extant shares may appoint whomever he wants to both the board and the executive staff. And, of course, can remove them whenever he cares to. If his son is the legal owner of those shares on paper, perhaps he sold them to him (or gifted, or whatever). What's the issue here?
Olympiakos is arguing that he gave someone loans to buy Xanthi, either through this company or through other means. Haven't seen any proof of that.
I believe the below is the same DIMERA, which also gives mention of the cash infusions Savvidis is making (increase of nominal capital; aka, issuing additional shares that he "buys" from the company).
https://opencorporates.com/companies/cy/HE170432