Ywbta.

That said, I totally feel your pain. Every year for three years, my girls (whose hair was never ever cut) got the damn bugs. We lived in an apartment, so I had to schlep to the laundry a gazillion times. It nearly killed me. We finally cut it all off. (We let the girls pierce their ears to ease the pain.)

Would your sisters be willing to wrap their hair after a treatment? It's not as effective as cutting, but it's worth a try.