I was in pretty much the exact situation as you with two brother kittens when I was in 4th grade. They had really bad fleas, so my brother and I gave them both a bath. They both ended up going into shock from the water. One died at the vet - the other lived to be able 21.
Please don’t risk it. I’m in my 30s now and still don’t forgive myself for Ernie’s death.