This cipher is quite difficult with the amount of information available here.
Wartime cryptanalysts expected to be able to solve for the keywords after
150 to 200 plaintext-ciphertext pairs were established. Solving this problem
probably requires trial and error to guess the correct period for segmenting
the message, and also to guess which key was re-used.

The second square of the Double Playfair used one of the keys
listed as possible duplicates: BRIGHTONROCK, in left-to-right rows.
The period chosen is 15, so that the cipher is broken up into pairs thus: