ISIC for our boys???

We never did, how old are boys, my kids brought their school id cards but never used them,are you boys adults( over 18?) Will they be staying in hostels?

We got one for our daughter who had just graduated high school and was 18. She didn't have a school ID card. It did get her discounts in some places. It's been three years so I can't quantify it anymore, but at the time I remember thinking it was worth it.

The boys will be 15 & 16. They will have school ID's, but I wasn't sure if places in Europe would accept those. So,
Just take their US school ID's?

15 and 16,, just bring school ids.. not sure what countries you are going to visit , but in Paris for instance all kids 17 and under are free at many museums.. my kids were never asked for id.. but they were young enough ( 14 and under) that they did not appear close to cut off age.. your sons probably look a old enough that you should make sure they have proof of age.. a copy of their passport and a student card will work fine in most places.. or a drivers licence if they have it..

I never bought international ID's for my kids. I'd always ask for reductions and/or student tickets. Generally, the vendor saw the age of the kids and didn't ask for their own student ID's. The only time I ran into resistance were some sights in Italy. They only gave discounts to Euro union residents, in which case my kids still wouldn't receive a discount because they're American. I never ran into a situation where an international ID would have helped.