wifi low bandwidth

my name is sajeesh , iam a beginer with mikrotik also with wireless connectivity. i used mikrotik devices to connect one head office to 5 branches for that purpose i bought two rb 433ah .6 r52 350 radiocards ,4 sxn 5hnt, andrew type grid antenna,cat 5 cable , maximum air distance is 5 km .for linking 5 branches i put one rb 433 ah in the HO and one rb 433 in the central branch ,first i put ho to branch 2 where i use sxn ,air distance is 3.2 km, los, i got 25 mb through put[ 69 db signal].then i put a link between two rb 433
i got one end with 67 db signal [h.o. end] and a through put of 25 mb but the another end i gets only 77 db signal and a through put of
13 mb but i need more speed in this link because this link works as a repeater station ,los ,3 km distance .i believe this is because of my unawareness in router setup so pls help me to do this job perfectly.one more question is the wireless connectivity can use as a core banking connectivity for banks ( is any security prblm for banking data) i am a beginer so i need detailed reply

hi,

which country are you from? which wireless protocol are you using for communication?

do you have any diagramatic representation for your case?