Is it incumbent upon the questioner to sacrifice his current job abroad and leave it for his brother in order to return to his home country and care for his parents and unmarried sisters, or should he remain in his current job?

Traveling in search of livelihood is permissible as long as it does not lead to something forbidden, such as neglecting the rights of parents or traveling to lands of tribulation. Honoring one's parents is among the deeds most beloved to Allah. Prioritizing others in worldly matters is commendable altruism. When hesitant between proceeding and refraining from a permissible matter, one should perform Istikhara (prayer for guidance), seek Allah's help, and then consult trustworthy and sincere people. If you find work in your country that suffices you and your dependents, then remaining with your family is better. Otherwise, endure the expatriation until Allah facilitates your return.