We have found that the best way to do this is to create a new site in the name of the merged club, copy the member database and any league registrations from the constituent sites to the new site, and then make the sites of the merged clubs inactive. The admins of the new site can then create new teams and squads, and their league(s) can associate their competitions and fixtures with the new site.
This approach allows the merger to take place with the minimum of data movement, allows players to retain the stats that they already have associated with their records with the separate clubs and have stats from the 'new' club added to those, allows the 'new' club to start with a clean sheet, and also allows the merger to be undone quickly and easily should that be necessary. It also keeps any history with leagues accurate, as that will remain associated with the separate clubs.
Please contact us with details of the two clubs concerned, and the name of the new club. You should also make your County Board aware of the merger, as they also have systems that will be affected, and any leagues of which your are a member. If either club, or both, has Clubmark accreditation then you need to involve your County Board as accreditation is granted in the specific name of the club concerned