What is the maximum number of cabin crew members on an A320 load sheet?
I believe that there are six crew seats in the A320 cabin. as long as the operating crew occupies these seats they will be included the crew figures for loadsheet purposes. In the event that these seats are occupied by non-crew they will need to be included manually. Not really common nowadays but it was routinely done in the 90s.

In the event that there is crew occupying a passenger seat (deadheading) they will be trimmed as a passenger.

The reason is most loadsheet programmes will adjust the Dry Operating Index  (and dry operating weight) depending on the number of crews entered in the crew field (eg 3/5). If a crew (deadheading or otherwise) is occupying a passenger seat, the system will only be able to account for this person if he is checked in.

Depending on the airline and the local country regulations it may not be possible for deadheading crews to travel on the General Declaration, instead they may be required to have tickets and be included in the passenger manifest. 

To summarise, everything on the airplane must be accounted for, both in terms f weight as well as its effect on the trim, irrespective of whether it is a person on a jumpseat or passenger seat. 

Hope this helps.