“They can fight her alone”. No they can’t, that’s why Oda has them literally double teaming her and still almost near death.
Laws Takt came from the Kid distraction then while BM was distracted by Takt he hits Kroom, so it all starts from Kids distraction. Then when Kroom hits BM is injured but attacks Law, while distracted against Law Kid builds his gun and attacks BM. They’re clearly using teamwork as well as seen by Law calling Kid to hit her with the finisher.