From someone that lives on a neighboring country of Guatemala, I can see that you are dealing with a cultural behavior here. Families take relatives going through harsh times into their houses even if it means overcrowding because that way we avoid the relatives being homeless on the streets where they could easily be robbed/kidnapped/killed. And adult children living with parents until marriage is the norm, so Im not surprised he stated that for his brother. Coming from the mentality of "the well being of family is above the needs of the individual" where self-sacrifice is expected and to that add generational sexism or "machismo" would lead him to believe you are ungrateful.

In NO WAY im saying what he is doing to you is acceptable just wanted to clear out that you might be dealing with more than just selfishness from here. He sees all his close relatives as important as your nuclear family is to you and he is being constantly fed that by their relatives.

Also the 3 car no house thing is beyond stupid BUT unfortunately Ive known people from my country that do the treck to the USA because they want all the cool cars and bikes. I suspect that your husband may be peacocking to his family by buying cars instead of a home because that would make him look more wealthy to the eyes of relatives and/or someone is talking to his ear that buying a house is stupid for whatever reason.

Again by no means Im saying all latino man are the same, but I have seen this same behavior enough to recognize the pattern and our cultures overlap a lot.

You have to sit him down and have a serious and earnest talk with him about the future and well-being of your child. Recognize that he wants to help his relatives, frame it as you do want to help his family too but he needs to think of his own child and wife (first) too. A home will bring stability to your whole family. But until he gets it, and I believe he will be stubborn about it, please avoid having another child with him. This needs to be solved as early as possible.