In Dec 2009, the 9W booth at international terminal wouldn't take my luggage for the continuing domestic flight. They said "new security rules". I had to take them on the bus to the domestic terminal and check them there.

I don't know if the reverse is different.

To the OP: if your family does have to carry the luggage, of course the bus takes luggage of any reasonable size (if the airline will accept it, it is not an unreasonable size). There is much less hassle nowadays because of the shuttle. There's even someone on the bus who helps with the luggage and does not appear to be hustling for tips. Takes a little time though, what with the queueing and showing boarding passes and so forth.