Who to combine/merge two iTunes folders without duplicates

We use two MacBooks in our household, each accessing their own iTunes library

- although 95% of the music is identical (= rips of our ancient cd collection).

We are hoping to merge these two libraries now - if possible, without creating duplicates.

Current scenario:

Macbook #1: iTunes accesses iTunes Media folder on external drive

MacBook #2: iTunes accesses iTunes Media folder on internal drive

Planned scenario:

- merge ALL music into iTunes Media folder on the external drive, freeing up valuable hard drive space on MacBook #2

- avoid duplicate songs (most songs are present in both iTunes Media folders - mostly my old cd collection & some iTunes purchases from shared account)

I don't need to preserve any plan lists / counts from MacBook #2's iTunes, so what is the safest way to merge/combine these two libraries?