Update 2023: This is not allowed. On the Malta Public Transport website it says:
This card can be used by a single person for 12 journeys on day
routes, 6 journeys on Tallinja Direct Routes, Night Routes and other
premium services, or else a mix of both.
This was also confirmed by their online support ([email protected]) on June 27th 2023:
Kindly nothe that the Twelve Single Day Journey Cards include twelve day trips or six night trips or six trips on TD routes. These cards cannot be shared. These are easily bought from our ticket
booths and cost €15. Any unused trips for Twelve Single Journey Cards
are not refundable.
Credit:stackoverflow.com‘