I had the same issues with Ares my 5yo black/tan male. When his housemate/sister was diagnosed with osteosarcoma and had her left rear leg amputated back in Feburary. Ares became more aggressive and dominate. He even started to try to mount his housemate/sister Sasha 6yo Husky. Usually he’s very shy and reserved and always follows his sisters not visa versa. I think since he knew Daisy, alpha female, was sick he needed to step up his game..?