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. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no doubt that what you mentioned about your brother is very serious since he does not perform the prayer and does not fast. Therefore, all of you are obliged to advise him and remind him of Allaah because the prayer is the most important pillar of Islam after the Two Testimonies of Faith, and abandoning it is an act which takes a person out of the fold of Islam, according to the view of many scholars . Abandoning the obligatory fasting is also a very serious matter.
Therefore, we advise you to follow the following steps in advising him:
1- Supplicate Allaah earnestly to guide him and enable him to do good as the hearts are in the Hands of Allaah and He turns them the way He wants; especially the supplication of his mother as it is among the supplications which are answered. The Prophet said: "There are three supplications that will undoubtedly be answered (by Allaah): The supplication of a victim of injustice, the supplication of a traveller, and the one of a parent for his children." [Ibn Maajah].
2- Persist in advising him with wisdom and in a good manner to perform the prayer and fast. In this regard you may make use of beneficial tapes and books.
3- Try to get him out of his loneliness by finding a pious company for him, who would help him in better adhere to the religion and help in his worldly matters.
4- Look for an appropriate job for him even if it is a light or symbolic job because loneliness worsens the matter for him.
5- Perform Ruqyah on him using verses from the Book of Allaah and authentic supplications from the Sunnah of the Prophet as he might be possessed by jinn and the like. For more benefit, please refer to Fatwa 88660.
As regards giving optional charity for him while he is not performing the prayer, then this is permissible even if we are of the view that a person who abandons the prayer is a disbeliever, because it is permissible to give optional charity to a non-Muslim according to the view of the Hanbali School of jurisprudence, and the well known opinion of the Shaafi'ee School of jurisprudence and the view of some scholars of the Hanafi School of jurisprudence . However, if it is known that he will buy something forbidden with the charity that is given to him, like cigarettes and the like, then you should not give him the charity as in this way you are helping him in sin. However, it is permissible to buy medicines for him as this is not helping him in sin, unless the medicine itself is forbidden.
For more benefit, please refer to Fataawa 92179, 86864 and 85229.Allaah knows best.