Josh was 1 when we got Eika as a pup, so it's really hard to try and think of any advice. But something that may help, is it possible to take him on a really long walk and make him really tired (plus getting some 1:1 time) and then try introducing again? And definitely keep on a short leash for now, which i can imagine is difficult. Goodness, doesn't rain but pours hey.
And as others have said, a professional, if you can get a good one, sounds like a must.
ps, really glad she's home xxx