Learn French: Ils sont souvent drôles.

Adjectives in French must match the noun they describe. Because the subject Ils (They) is plural, we add an "s" to the adjective drôle to make it plural too.

Do I pronounce the "s" at the end of drôles?

No, the "s" added to make an adjective plural is almost always silent. drôle (singular) and drôles (plural) sound exactly the same!

Would drôles change if the subject was feminine (Elles)?

No, it would stay exactly the same. Normally we add an "e" to make an adjective feminine, but because the base word drôle already ends in an "e", it doesn't change. We just add the "s" for plural: Elles sont souvent drôles.

Why is souvent placed in the middle of the sentence?

In French, adverbs like souvent (often) usually go directly after the conjugated verb (sont).