Osimhen as said by their president in Dicember is already sold but we dont know to whom.
A reason on why we dont know yet is because it may go to EUA and there the market session will start in 1 week.
It may also ends at PSG, they needs to replace Mbappè somehow even if they are not spending so much money lately.
So TLDR, Napoli will have the money from Osimhen and they can spend for Lukaku.
If it's true as you say, that doesn't mean there is a possibility that PSG has already signed Osimhen because apart from Chelsea, it is likely that PSG is the only one who wants to spend a lot of money. For another club, Real Madrid may have that kind of funds but they have already got Mbappe, so it would be almost impossible for them to sign Osimhen.
Everything will be clear when the truth is revealed but somehow I feel that the club in question is PSG.