Is the son obligated to bear the sole responsibility of caring for his mother for 18 years without the participation of his siblings?

Your housing and care for your mother is a great act of devotion, and kindness to parents is one of the greatest doors to good, its benefit returning to you in this world and the hereafter. You must seek your reward from Allah, even if your siblings do not appreciate your kindness, for "And whatever good you put forward for yourselves - you will find it with Allah. It is better and greater in reward." (Quran 73:20) Providing for parents is obligatory upon all children, and you should discuss this gently with your siblings to explain their responsibility to them. If they do not respond or do not have the money, then the responsibility remains solely with you, and it is not permissible to abandon your mother.