In medieval and Anglo-Saxon times, it was normal and accepted to name siblings (multiple or singleton) with the same element, in your case
bert.
Today, however, such a thing is not liked. It's seen as confusing, and potentially damaging to the process of individualisation amongst siblings (especially multiples).
Personally, I agree with today's view. I am, however, fine with the practice if it's for a sibset in a historical story. (Though triplets are exceedingly rare naturally: only one in 8,000, on average.)
Miranda
"Come... you must eat my child." — From a badfic
Proud adopter of 15 punctuation marks; see my profile for their names.