I'd acquire Butler and wouldn't give it much thought. He is a very good 2 way player in the same tier as Irving and Hayward in the league.
It would probably mean that Horford would have to be traded next summer, but I'm ok with taking the championship shot this year.
And I would absolutely trade Brown in the trade if that is what it took.
So basically Butler for Brown, Morris, Yabu, and Nader (I think that is enough salary but if not add Semi).
Post-Trade - Main 2 deep rotation
PG - Irving, Rozier
SG - Butler, Smart
SF - Hayward, Tatum
PF - Horford, Theis
C - Baynes, Williams
That team if everyone is healthy and back to where they were would be a real threat to the Warriors and the very heavy and clear favorites in the East. Even if the Sixers acquired Leonard (for basically Saric, Covington, and 1sts) that C's team would still be the favorites in the East.
I'm not mortgaging a potential Eastern Conference / NBA dynasty for 1 year of still-underdog contending status against Golden State. That roster won't win it.
If Kyrie insists, then we can get a lottery pick + at least 1 good player or prospect for him.
Plus Smart, Williams and our Kyrie haul is a very good and still young core moving forward.
We'd also have 3 good-to-elite lottery picks (Sacto, Memphis, Kyrie lottery pick) to use or roll over to ideally go after a PG, a big and another wing. Personally, I don't think Rozier is the answer at PG, and I'd like a PF/C to hedge against Robert Williams not turning into Capela.
EDIT - I would try to keep Kyrie here at nearly any cost- except trading JB or JT.