Well, first of all you're not going to have much luck putting anything on keys 9, 10, or 11 of a 5320 (it's only an 8-button phone.)
In general you can copy keys from one set to the keys of one or more sets of the same type: PROVIDED THAT THE KEYS ON THE DESTINATION SETS ARE UNASSIGNED.
In MCD 4.0 (or earlier) you can select "Copy Keys" on the multiline set key assignment form. (In MCD 4.1 this is on the "Keys" tab of the "User and Device Configuration Form".
Check the checkbox on the keys you wish to copy, and in the destination box list the prime DNs of the phones you wish to copy the keys to (example: 5529, 5537, 5600-5630, etc.)