I think I see what's required but I haven't done the puzzle (so your checking letters might prove me wrong). The pairs could be -
24a British comedy duo [2nd word 4 letters & 'lives' = IS].
28a sweet+sour drink [1st word 4 letters].
25d an old fashioned means of road transport [2nd word 4 letters & 'tights' = a general word for stockings etc].
11d mythical lovers (one died swimming to meet the other)[1st word 4 letters & the King is biblical, minus last letter].
19d a phrase meaning 'before everything else.'[1st word 5 letters & 'duke' = FIST].