Me and my family are going to HK Disney land for 1 day only

You can take any "A" or "E" bus routes to Lantau Link Toll Plaza and change to take Route R8 to reach the Disneyland directly.
The R8 costs arond 7HK$. For the bus fare for the "A" or "E" route, it is hard to tell. As far as I know, the bus line A21 costs about 26HK$ per person, but the E routes are much cheapers.
For the back trip, you can use the same way.