Formal:
* Bem-vindo(a) ao lar! (This is the most literal translation, using the formal "bem-vindo" for a single person or "bem-vindos" for multiple people)
Informal:
* Seja bem-vindo(a) em casa! (This is a more common and friendly way to say it, using the informal "seja")
* Bem-vindo(a) de volta pra casa! (This means "Welcome back home!")
* Que bom te ver em casa! (This means "It's good to see you at home!")
You can also use "Voltou pra casa!" (You're back home!) which is a more casual and friendly expression.
Remember to adjust the gender of the pronoun "você" (you) depending on the person you are addressing.