Learn Croatian: Obitelj ju puno voli. - The family loves her a lot.

Ju (her) is a short-form pronoun, also called a clitic. In Croatian, these short, unstressed words follow a strict rule: they must sit in the "second position" of the sentence. Here, it naturally takes the second spot right after the first word, obitelj. You cannot say Obitelj puno voli ju.

I learned that the short form for "her" is je. Why does this sentence use ju?

Both ju and je are short accusative forms of ona (she). While je is the standard default, ju is also very common. Ju is strictly required when the sentence also contains the verb je (is) to avoid awkwardly saying je je, but many speakers use ju interchangeably with je in other sentences like this one, too.

Is obitelj a masculine noun because it ends in a consonant?

No, obitelj (family) is an important exception. While most nouns ending in a consonant are masculine, obitelj is actually feminine. It belongs to a special group of feminine nouns ending in a consonant that you simply need to memorize as you encounter them.

Why do we use voli (loves) instead of the plural form vole?