If stack & reach isn't the best method of comparing two bikes, then what is?
Letting your kids try it out, which I do realised not an easy feat considering Islabikes doesn't have a brick and mortar shop (Unless that have changed).
Speaking to Islabikes directly would help greatly.
I don't understand how the fact that kids grow quickly, means that comparing two bikes is irrelevant or unnecessary:
Clearly the 26 would be a better buy, as he will grow out of it more slowly, but not if it is too big for him now.
If stack & reach isn't the best method of comparing two bikes, then what is?