What if Peter and Gwen run into Leo, Raph, and Donnie before Mikey and Miles meet up and they're like... they fight at first. B3cause three scary mutant turtles normally aren't a good thing to the spiders. Its a misunderstanding that leads to a pretty quick conflict, mainly cuz the fighting was gonna get them caught.
Like imagine Leo locked in a headlock and suddenly going
"Wait wait! Stop!!! You're gonna get us caught!"
"Uh... that's kidna the point!?" -Gwen
"No! I mean... by our baby brother!!" -Leo
And that's suddenly makes them realize that oh. They aren't enemies. They're jsut kids who are sneaking out snd following their little brother around, just like how they're following Miles.
This is literally how I imagine it going. It’s completely the turtles’ fault for thinking the Spider gang is an enemy, but to be fair, what else are they supposed to think!? They’re completely convinced whoever Mikey is meeting up with is out to get him. The Spider gang thinks the turtles are planning to ambush Miles and it’s a whole mess.
But ultimately they all realize oh, this isn’t even remotely what they think, it’s puppy love. The turtles are sooo embarrassed because wow, it’s SO obvious in hindsight, and apologize to the Spider gang while also getting a quick explanation as to what’s going on. They agree it’s harmless and either go their separate ways, or get caught for stalking, whichever works for the funniest outcome tbh