What to do when you have obtained very similar results with two different groups and you want to publish them both
I'm surprised you did not mention the option that I would probably do: combine all data into one paper. Based on your description it sounds as if both data support a similar hypothesis/line of enquiry. If that is the case, publish one much stronger paper using two independent sets of data. All authors would need to be included. You could check with both teams to see if they agree. Speaking of which, have you asked them what they want to do?