Bechoros 18

Rabanan holding ei efsher litzamtzem even bidei adam,what does Reb akiva mean when he says in the mishna mishmanin beineihen,in a safek if there's a bchor Reb yosi patu bmatanos aino zocheh kizocheh,and why we needed three cases of the machlokes Reb akiva and Reb Tarfon