@JWChibi
It depends on what country's royal customs they took inspiration from.
In France,for example,from the 1600 to the 1800 children did not live with their parents. They live in a separate place sometimes their own smaller palace and were raised by wetnurses, nannies,what we now call butler and thought by a
plethora of preceptors. (Here they replaced the preceptors by a boarding school). They would see their parents from time to time (that's depended on if the parents wants to see them or has the time) and would only join "society" and stand along side their parents when they were deemed mature. For boys,it was when they were considered man enough which does time varies from age 14 to 16 and for
girls when they were of a marriageable age. They would usually be presented (girls specially) at a ball given in their honor and to celebrate their "adulthood".
This manga also takes inspiration from modern day Japan (where adulthood is at 20 years of age). In this it will probably be when they finish school.
So if we take those in to consideratio
n,they probably don't get to see their adult siblings often and Bakarina has not seen them since she is probably not permitted in royal society yet.
They mixed a bunch of customs from different countries so the normal nobles like her seem to have a lifestyle in between Victorian era England and Germany (where children lived with family). So the royals are more French (with obviously Japanese mixed into it ) while the nobles are more like regular families with Victorian era customs.