Merges are essentially made between 2 individual profiles, not between tree branches. Each duplicate pair of individual profiles must be processed separately.
Before you approve (or reject) this merge, you should review this page:
Be sure to check the various links on the page for additional or more in-depth information about the merging and matching processes and procedures.
Also, remember that the correct Last Name At Birth must be determined first when the profiles have different LNAB spellings! You may decide to set the proposed merge to an unmerged match to allow for additional research time.
Finally, remember to collaborate with the other profile manager, if possible. In this case, the other manager doesn't seem to be active (last logged activity was on 18 Aug 2015). You may want to submit an Unresponsive Profile Manager form to deal with that.
I believe the preferred method is to find any duplicates for the direct ancestors before you process the merge in question. If the parents. grandparents, etc. have duplicates, those should be merged first; then work forward to the merge in question. This method will keep all related parties connected for succeeding merges.
Merges (the aforementioned succeeding merges) for duplicate spouses, children, and siblings can be completed later.