Which instances in act 3 where each young person mentions this willingness to die if they are separated?

Answer 1

When romeo is talking to friar lawerence he says id rather be killed than banished from my juliet

Answer 2

In Act 3, Romeo declares his willingness to die rather than be separated from Juliet when he says, "And, for that offence, immediately we do exile him hence” (3.1.188). Juliet also expresses her willingness to die rather than be separated from Romeo when she says, "If all else fail, myself have power to die" (3.5.242). Both Romeo and Juliet are willing to go to extreme lengths to avoid being separated from each other.