All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
There is great dispute among the scholars about the ruling on providing for relatives, including brothers. The strongest opinion in our view is that of the Hanbali School of jurisprudence - that it is an obligation to provide for them under certain conditions. Ibn Qudaamah said: “The adopted view of our (Hanbali) School is that an heir (i.e. a potential heir) is obligated to spend on his relative if he is entitled to inherit from his estate (in case of his death)." Before that, he mentioned three conditions under which one is obligated to spend on his relative saying: “First, that he [the relative] is poor, having no wealth or earning potential; second, that the one who is obliged to provide maintenance has extra money after providing for himself, either from his wealth or his income; thirdly, that the one who provides maintenance is a legitimate heir [in case his poor relative dies].” [End of quote]
Based on this, it should be realized that your husband is not obliged to support his brother because he is excluded from inheriting from him because of the existence of the father. For more benefit, please refer to Fataawa 147839 and 85715.
However, if your husband wants to be kind and dutiful to his parents by helping his brother, then this is good. It should be enough for you if your husband fulfills his obligations towards you and your children. Indeed, the right of the parents is great, but it would be good for the parents not to help their lazy son to be a burden on others, and they should not be a nuisance to your husband by overburdening him to do more than he is able. For more benefit, please refer to Fatwa 181219.
The lazy brother should be advised to work and endeavor to make a living for himself. In addition, the Ahaadeeth about the virtue of seeking one’s own livelihood should be clarified for him. Al-Miqdaam narrated that the Prophet said: "The best food a person eats is that which he earns with his own hands, and the Prophet Daawood (David) used to eat from what he earned with his own hands." [Al-Bukhari]
Finally, we would like to comment on the house inherited from the ancestors: if your husband has a share in it, then he has the right to claim his share.
Allaah Knows best.