This second person pl
You (all) drink = mwanywa
You (all) don't drink = hamnywi
But here we have a negative Imperative.
Neg. Imp. Sg:
U + si + stem (if last letter 'a' it changes to 'e' )
Usinywe - Don't drink !
Neg. Imp. Pl
M+ si + stem (if last letter 'a' it changes to 'e' )
Msinywe - Don't drink (you all) !