My father passed away I received a check made out to his estate for $800 from his landlord.

No, you should not be able to deposit the check into the joint account, because that became your account at your father's death and his estate has no interest in it, while the check belongs to his estate. If there really aren't any other assets, and if you are the only heir, you can try to have the landlord make the check out to you. Otherwise, you may need to do one of two things (assuming your father had his principal residence in Georgia--if not, this may not be the correct answer): either file a Petition for Order Declaring No Administration Necessary asking that the check (and any other assets your father owned, such as his personal possessions) be distributed to you, or open a probate estate (either as Administrator if there was no Will or as Executor if there was one) and deal with the check that way. I realize that this isn't a great answer, but unfortunately this sort of situation happens all the time.