Say i have 300$ on my paypal that i recieved from someone, if i send that money to a different PayPal and he charged back would it charge back on both paypal accounts ?
It would only charge back on the PayPal it was sent to. You would have a negative PayPal balance. Or they would try to take it out of the credit card / bank account, if you have one on the account.
The second account that the money was sent too would be untouched. But the original account it was sent too then chargedback on, would be extremely fucked AKA: in the negative if they were to win in their favor over the dispute.