How do you know which subject pronoun to select for a sentence? For example, ellos goes with "Brooklyn and Drew". How do you know if you are right?

Okay males are always "El"

Females are always "ella"

So if its all females you have "Ellas"

If there is a male present "ellos"

In spanish if one male enters a group with females it is "ellos"

You know you are right with practice and double checking things like this.

You also don't say "El mesa" you say "la mesa" pay attention to what the word ends with.

hope this helps and btw im a native Spanish speaker so it's all correct :) !!