here the same meaning as - нельзя - it is not allowed, must not . but word никак strengths expression from нельзя . so i guess you could translate as it is not allowed at all.
То , что мы забрались в чужой сад -это было пол-беды . Но уж никак нельзы было громко смеяться обрывая чужие яблоки .
It was jut half problem that we penetrated in the garden that did not belong to us , but we had not to cry and laugh picking neighbour's apples
Никак нельзя could strength question changing one to demand
По-тише никак нельзя ? would you like do not cry ? to be calm .
or sometime it could make request more polite , so it would sound as not demand. А никак нельзя ещё одну тарелку принести . it is possible to bring me one more plate . The difference between the last two cases determinate from the tone of voice , но никак не структурой прtдложения ( никак не other structure you can meet)