Neither is correct. You could say 'Brazilians are warm/ Brazilians are warm people.' Or maybe 'warm-hearted'?

The word "warmfull" does not exist and if it did, it would probably have one L at the end. There is "warming" and that's simply something that warms or a process of "warming your food" or in "global warming". For Brazilians, you would just say that "they are very warm people". I've met many and almost all of them were very friendly. Brazilians tend to be energetic as well, so I'd probably save "warm" for some folks that are more mellow and super nice, like many in the southern United States are.

Camila, You could also say: Brazilians are pleasant people; or: Brazilians are lively people. It all depends on what characteristic of the Brazilian people you would like to focus on. "Warm" people can have many different meanings, and the sentence should show the context. Therefore a longer, bit more describing sentence, especially while you are still practicing the language, will help in us to better guide you. Keep on trying! You are doing well!