Is it permissible for a husband to leave his wife, his young son, and his sick father, and travel to infidel countries to achieve his dream of obtaining citizenship of an infidel country? And is he who helped his sister live in infidel countries sinful?

It is not permissible to obtain citizenship of a non-Muslim country except in cases of extreme necessity. A husband is not permitted to be absent from his wife for a long period without her consent; if he does so, she has the right to seek a divorce. If the husband's father falls ill and has no wife, his children are obligated to serve and care for him; if they are unable to, they should hire a servant for him. As for a sister residing in non-Muslim countries, specific conditions must be met. If these conditions are fulfilled, her residence and assistance for it are permissible; otherwise, assisting her is not permissible, with the caveat that a woman is not permitted to travel without a mahram.