I wasn't sure we were going to make it- Sergeant Sassy Pants cried and growled and fussed non-stop and couldn't be left with anyone unsupervised. But we stuck it out and realized she was all growl and no bite, We stopped reacting to her protests. Well, I stopped reacting to her protests... cause Captain never did worry about the noises. Sassy Pants will initiate play and then scream as if she's being murdered when someone wrestles back... but she really is having fun. They could sometimes even play together without the ruckus. And then, they became friends! These sweet moments are even more special after all the worry!
11/28/21 update
Sergeant Sassy Pants and Captain Oblivious have signed an agreement, which is temporarily nullified by Sergeant if it is treat time or her preferred toy time. She still raises a big stink if she thinks she has to share anything she feels belongs solely to her. But they do cuddle, groom, and play with the normal toys very nicely together. But that poof ball... 100% off limits to anyone but Sergeant!