Well they are already very rich men. We can offer them both a deal of say £200k a week with a get out clause if we fail to make the top 4. We can pay them both £10million signing on fees, safe in the knowledge that we either have them for 3/4 more years OR we sell them for a sizeable sum in the summer. Everyone wins.
And if Pep wants Sanchez that much he'll put that deal on the table. They don't see Arsenal as rivals and Aguero won't play much this season because of Gabriel Jesus (unless he gets injured again). The only issue for Arsenal is that he's 29.