Peeta is frustrated with both of them and wants them both to fuck off, tbh! But he's too nice for that. I imagine Prim would feel bad for Katniss since she's obviously upset about Haymitch, and she'd feel bad for Gale because she knows he didn't mean to cause a fight on purpose. She'd probably be like, well what did you expect?? It's Haymitch. But yeah, she would be sympathetic and probably try to get Katniss to forgive him because he's her ally and all.