What do you mean by "Sync"?
Main purpose is to ensure that what changes are made on one MacBook are replicated on the other and visa versa.
The vice versa is the always going to be a problem.
The general term means when two Libraries (A and B) are compared and files in Library A are copied to Library B, while files in Library B are also copied to Library A so that both Libraries are identical.
This is bi-directional copying and you cannot do this automatically with iPhoto. No Syncing software is capable of parsing the iPhoto Library in this manner. One or both of your Libraries will be damaged if you try this.
You can have uni-directional copying - files in Library A are copied to Library B - this is essentially backing up. Obviously you can also copy from Library B to Library A.
The nearest you can get to syncing is to use iPhoto Library Manager to move files/Albums/Events plus associated metadata between Libraries. This process cannot be automated.
I would note that the upcoming Photos app and the iCloud Library feature may make this possible.
Thank you for the advice. I am not a whiz on computers so bear with me. Before I commit to iPhoto Library Manager can you answer the following questions:-
Will iPLM allow me to duplicate my current photo library on laptop A (i.e. there will be 2 full photo libraries on A) and then merge one of the libraries in A to the photo library on laptop B? I presume that I can also duplicate my iPhoto library in laptop B and keep one copy in each laptop as 'fallback' set of photo data whilst I play around with trying to merge photos. I appreciate the risk of losing photos - something I do not want to happen - maybe I can back up each library (a and B) to my external hard drive (Apple Airport Time Capsule).
If you can expand on my query above I would appreciate your advice.
Will iPLM allow me to duplicate my current photo library on laptop A (i.e. there will be 2 full photo libraries on A) and then merge one of the libraries in A to the photo library on laptop B?
Yes. You can duplicate a Library in the Finder, no need to Library Manager there. And yes you certainly should back up both Libraries, absolutely.
There is an app that will sync two libraries together. However, it only will sync original/master photos and not any edited versions, keywords, titles, or other metadata. It's is manual or automatic, i.e. A ⇄ B, or it can be from A ➙ B or B ➙ A. The software has to be running on both computers at the same time with the two Macs connected. I've not tired it but there's a 7 day free triial you can use. It's called SyncPhotos.
If you try it be sure to have a current backup of both libraries before you start. It would be best to be hard wired connected between the two Macs but you can try the wireless as long as you have backups.