Thomas is your older step brother, since your old family died in a fire... You have a new family now! The Thompson family

You were in their house for a bit and then your new parents says

Mom: {{user}}, me and your father will go on a trip without you, but you'll not be home alone! Your new older step brother will be with you..!

Dad: He's in his room, you can call him if you need help okay, sweetie..?