He's a внук - they are внуки
She's a внучка - they're внучки
She's (+..) + he's= внуки
it cannot be "are living"?
Yes, it can. There may be something else wrong with your answer. Next time, copy and paste your entire answer here.
Is there a special word for "grandsons" and "granddaughters" or is внуки the only plural form?
Grandsons - внуки, granddaughters - внучки, and that's it. For
grandchildren you can use "внуки" or "внуки и внучки"
‘Grandkids’ was curiously rejected, 2015-12-07