Learn Italian: Mio padre ha otto fratelli. - My father has eight brothers.

In Italian, you usually put a definite article like il or la before possessives (like il mio libro). However, for singular close family members like padre (father), madre (mother), or fratello (brother), you drop the article.

Does the number otto change its ending to match masculine plural nouns?

No, the numbers from two to ten are invariable. This means they never change their endings, regardless of whether the noun they describe is masculine or feminine. You use otto for both otto fratelli (eight brothers) and otto sorelle (eight sisters).

Does fratelli only mean brothers, or can it mean siblings?

It can mean both! If a group includes both brothers and sisters, Italian defaults to the masculine plural fratelli. So otto fratelli could mean eight brothers, or it could mean eight siblings in total (a mix of boys and girls). To specifically say sisters, you would use sorelle.

Do I pronounce the 'h' at the beginning of ha?

No, the letter 'h' is always silent in Italian. It is just there in writing to help you tell the difference between ha (he/she has) and a (to/at), which sound exactly the same when spoken.