Summer grasses / All that remains / Of soldiers' dreams. - Basho.
In the same square there are:
German Bomber A that's been tallied by British Fighter 1
British Fighter 1 that's been tallied by German Fighter B
German Fighter B that's not tallied by anything
How would this combat be resolved?
A single combined combat?
It's a multi-squadron combat resolved by the rules in 10.2, because there is a chain of tallies which involves all units (10.1.3).
Because there is a bomber in the chain of tallies, the Germans are the defenders (10.1.1).
Only if the German fighter had not tallied British Fighter 1 AND there was another squadron it had tallied would you have more than one combat.