@Rerechan8 correct the family titles are messed up.
they are su xi’s and the eldest brother’s parents and as such her nephew’s paternal grandparents
So they should’ve been greeted as father, mother and grandfather, grandmother. They somewhat erroneously translated 祖父 - zufu, 祖母 - zumu ( somewhat formal title for paternal grandfather and grandmother respectively. As opposed to the more informal pops and granny ) as great, grandfather and great, grandmother. It might’ve read better as respected grandfather and grandmother or just ignored
@Lorraine
As for the elder calling his son (blue sleeves) “brother”, they’re on crack. The word in the raw was 老大 -lao da ( Old-Eldest) which is an affectionate way to call the eldest child. ( Bonus If Su Xi is the 5th child she can be called lao wu Old-Five by her fam )