I always get confused on where to add ‘w’ in cases like ‘cɛ wɛrɛ’ or ‘denmisɛn cɛman bɛɛ’… I want to write ‘cɛw wɛrɛ’ but it is in fact ‘cɛ wɛrɛw’?
And ‘denmisɛn cɛman bɛɛ’… I would write ‘denmisɛnw cɛman bɛɛ’ but is it in fact ‘denmisɛn cɛmanw bɛɛ’?
I ni ce, Christy! Thanks for posting your question in the forum! 
I ni se!
So the short answer is that in noun phrases that have an adjective (e.g., belebele) or a determiner (e.g., wɛrɛ) than the plural marker appears not on the noun, but rather on the adjective/determiner:
Cɛ wɛrɛ → Cɛ wɛrɛw
‘Another man’ → ‘Other men’
As for “denmisɛn cɛman bɛɛ” (‘all the male children’), it is complicated by the fact that bɛɛ as a determiner frequently doesn’t require a plural (but sometimes we see people apply it in writing, perhaps under the influence of French pluralization practices). For instance:
Dugu belebele bɛɛ bɛ ji kɛrɛ fɛ.
‘All (the) big towns are next to water’
So there and in your question/example, you typically don’t need to add any -w!
That said, in some cases, the plural marker -w is added to determiners related to quantity; when that happens, it generally adds a degree of specificity. For instance, something like this sentence from a 1974 issue of Kibaru:
[…] npogotigi ka kan ka di jɔnni ma , cɛ sabaw ni ɲɔgɔn cɛ ?
'[…] the girl has to be given to whom, amongst these three men?