Initially, I felt BBP. Makes sense as well but thing is BBP won't save citizens...they would have sank both ships.
Also, you already have BBP ship at egghead and I don't see BB himself making a move just after beating Law.
So, it might really be RA because narratively and plot wise they are involved in the plot so them making an appearance to help Kuma makes more sense.
I mean throughout kuma"s backstory, RA were portrayed as helpless and doing nothing. I think this might be their chance to help Kuma and Bonney