Step daughter under weight

Apparernly my step daughter is only 28lbs at 4! Her mother does not see a problem with it, and says she's fine.

Her older sister was 25 lbs at one years one. Her dad thinks her mom is not feeding her enough. This is what the 4 year olds mother said

"She says born tiny first off, second off her doctor does not have a problem with her weight, and thirdly they have two different mothers! Most importantly they are different kids!"

I get what the mother is say, and they don't communicate well everything always turns into an argument! Fact is she's only 28lbs most kids do weigh more at that age!!

What do you all think?

There is there conversation from yestetday