The problem about Chslea for both players, Gavi and Osimhen is both players are attractive targets for many other teams but regarding Gavi, I don't think if Barcelona will lose this player easily because they have an 18-year-old player who can have a shining future and Osimhen can have much better options than Chelsea.
It seems like Osimhen will be the most wanted player in the transfer period that will come after this season. A lot of the biggest clubs will be interested to sign him. The last weeks made pretty obvious, that Bayern Munich for example really needs a world class number 9 again after Robert Lewandowski went to Barca. Thomas Tuchel is already looking for great strikers that could join Bayern for the next season and Osimhen is probably his personal favorite together with Kolo Muani from Frankfurt. I don't know if Real Madrid is also wanting to sign Osimhen this summer, because Benzema still has a contract for one more year and i doubt that Benzema or Osimhen would be happy to sit on the bench.