The two brothers have not fought at all this year they've been meaning more than 6 months of inactivity. The JBC, in accordance with their rules, have therefore taken both men from the rankings rather than allowing them to sit there taking up high ranking places.
This move is the latest in a string of JBC Vs Kameda brothers incidents which has, of course, seen the JBC strip the license away from the Kameda Gym and refuse to allow Shigeyuki Otake to become the president of the K3 gym. In effect this has left the Kameda's with out a home to fight from domestically with the JBC almost demanding them to transfer to a more trusted gym.
As for Tomoki Kameda, the current WBO Bantamweight champion, he is still recognised as a world title holder though he's not allowed to fight in Japan, just like his brothers. He's gotten around that by basing his next fight in the US though it appears that his bout won't be televised in either the US or Japan and it may end up only being shown on Thai TV of all places!
Although we won't second guess the Japanese Boxing Commission there is every chance that this this wasn't so much the JBC following their own rules as them again trying to force the Kameda's to either accept the situation they are in or force them out of the sport, at least in Japan.