Jesse F (22 TX Cav) and George Washington (31 TX Cav)Bone were twins. Their known siblings in service are: William (TST), Alfred Y (29 TX Cav), Young E (22 TX Cav), James P (22 TX Cav), and FM (Baylors Rgt. TX Cav). Doctor Matthew Bone was born in 1849 and so was probably too young to serve. The oldest brother John is an enigma.
There is a long gap between John and William, so there could be another couple of boys in there. Candidates are Caxy, GE, GR and Thomas. Leonidas does not seem to be related.
I can possibly get to 11 brothers, but not yet to 13.