Hi a judy ... the scheduled bus service will take them to
Benidorm Bus Station. Taxis and shuttle buses operate from there into the resort.
Alternatively, they could pre-arrange a shared coach transfer from the airport to their hotel (or immediate vicinity) with one of the many transfer operators mentioned here in this topic. Taxis or private transfers are also an option, but are obviously more expensive.
Weblinks, timetables and some approximate prices can be accessed on page 1 of this topic, a browse through later pages will let you read member feedback and opinions about the various options.
David