@deedet so it seems you don't understand what's happening here's tl;dr for you
(Single Hand Ryuuma) is not actually a real Ryuuma, When the 7th Brigade (Big Boss Ryuuma) Successor died that became the end, but they couldn't let it end that way, so he as a child was raised to become the next Ryuuma meanwhile the girl (Female Ryuuma) was also alive and became the next Ryuuma, BUT in the pillar raid there was also the 2nd Brigade (String Ryuuma) and his descendants/successor who he fought and died with, so at one time there was 4 Ryuuma
How? Check back to chapter 9&10 and see what Jin said to (7th Brigader Ryuuma)
But too bad nobody know that you're a fake so it's not actually clear who is an actual descendent from the first ryuuma or first Jin, since (7th brigader Ryyuma) actually replied back with
If i had to say, You're also a fake Jin
So the 2 Ryuuma (Female) & (Single-Hand) is actually from different line, the Female being the successor to (Big Boss Ryuuma) while (Single-Hand Ryuuma) is (not clear) king mayu new Ryuuma line, they couldn't let Ryuuma die so a new one had to be born
Also Jin & Ryuuma relationship is not explained now