Please. How to merge two families with same parents into one
Open the Families tab of the Records Window and select the two identically named Family records you have shown in your screenshot.
Then use Edit > Merge/Compare Records… to combine the two Family records into one.
BTW: If there is no Families tab use View > Other Record Lists > Families
Also you can enable the Families tab via Tools > Preferences > Records Window > Record Type Display Options
Open the Families tab of the Records Window and select the two identically named Family records you have shown in your screenshot.
Then use Edit > Merge/Compare Records… to combine the two Family records into one.
BTW: If there is no Families tab use View > Other Record Lists > Families
Also you can enable the Families tab via Tools > Preferences > Records Window > Record Type Display Options