Learn French: Tous les membres de la famille sont ici. - All the members of the family are here.

Tous is the masculine plural form of the adjective tout (all). It must agree with the noun it modifies, which in this case is les membres (the members) — a masculine plural noun.

Do I pronounce the 's' at the end of Tous here?

No, the 's' is silent in this sentence. When tous is used as an adjective in front of a noun (like tous les membres), you do not pronounce the 's'. You only pronounce the 's' when tous stands alone as a pronoun (for example, in Bonjour à tous).

Is the word membre always masculine, even if it refers to female family members?

Yes, the noun un membre is always masculine in French, regardless of the actual gender of the person it refers to. Because the grammatical gender of the word itself is masculine, we must use the masculine adjective Tous.

Why is it de la famille instead of just de famille?

Just like in English where we say 'of the family', French requires the definite article here. You need the preposition de (of) plus the definite article la (the) because famille is a feminine noun. In French, you can rarely drop the article before a noun.