"These mangos are not ripe enough" would definitely be the most natural. However you could potentially use both, but the difference is one uses the adjective "ripe" and one uses the verb "to ripen". If you did want to use the other construction, you would have to say "these mangoes haven't ripened enough" putting it in the present perfect tense. NOTE: "ripened" is not an adjective and so you cannot say "they are ripened".

'Ripe enough' is correct! You could say 'theses mangoes have not ripened enough' but that would require a clause, for instance 'these mangoes have not ripened enough to use in a pudding' and would sound slightly strange...:)