Escuan, I think the Harpy clue works as follows : a harp-like instrument, mean(S) to make music is the definition; the wordplay perhaps being AUK backwards, without U but with OR. In the next clue the definition is Lithuanian gel(T).
When you've got the grid mostly filled, you'll see that some of the interrupted entries have something in common. Just fill in the missing letters (in some cases 2 letters), then consider the Group B answers and entries in the same way. Once you've seen how it works, you'll quickly solve any unsolved B clues.