Maybe give each one of them specific hobbies they’re into and hint at maybe things regarding each of their back stories. Like maybe one LI wants to be a rockstar while the other is super into playing sports.
What I like to do when I’m developing a character (this comes from what I do for acting) I like to create a fake social media account, choose personality traits, aesthetics, accent, I dive 100% into the character. I try to become them. Once you research and become the character, dialogue will come easy to you!! Hope this helped!!
You can make them talk about their hobbies, memories (not necessarily relating to the mc but even from the li’s past).
I feel the li and the mc should have different personalities (even totally opposite at times). I personally really like such matches. Opposites attract each other, after all.