Edit: I did not at first see that it was Spanish. It's very similar to French.
If it was French, this would be your answer: "Tu tenes una familia grande."
Explanation:
Tuner is an -er verb.
To conjugate Tener remove the -er and replace with the correct ending for the form of the verb you are using:
Singular. Plural
Je tene (-e) Nous tenons (-ons)
Tu tenes (-es) Vous tenez (-ez)
Il/Elle/Ont tene (-e) Ils/elles tenont(-ont)
Although verbs most likely are different in Spanish, I hope my answer still may have been helpful.
