Okay so my sister is being deployed to Afghanistan for 6 months and I’m taking custody for her 2 yr…

Okay so my sister is being deployed to Afghanistan for 6 months and I’m taking custody for her 2 yr old. My nephew is not a fan of my 6 month old by any means! He flips out anytime he sees me or my mom holding him like full blown temper tantrum! I’m so nervous the closer time gets! Am I setting myself up for failure? I love my nephew so much but I can’t let his jealousy come between my son and I!!! Idk what to do!