Hong Kong Airport Single Trip Ticket

hello, i intend to buy single tickets for group of 3 from hk airport to HK station and from hk station to airport station because i think the package is cheaper.
the single trip tickets from hk airport to hk station can be bought at service counter in the airport,so where should i buy the single trip tickets from hk station to hk airport?

next, is free shuttle bus service offered from hotel to airport as well? if yes then the pick up point should be at e.g. HK station, is this correct?