cats that stil want to suckle

i have three four month old kittens who were still suckling on mum until they were three months old she now has a new litterand does not let them, but these kittens will suckle on my older cats how can i stop this, i have fourteen cats now and i live in Bulgaria.

The only way to stop them is to separate them from any cats who allow them to suckle.  Are your other females spayed now?  Sometimes a spayed cat who once had kittens will allow kittens to suckle her, but most of them will not. 

The cat they suckle is male and he does not seem to mind them suckling on him