What is the ruling on visiting a grandfather who has lost his memory due to old age, and is it obligatory to visit the mother along with traveling to her?

Allah Almighty commanded maintaining kinship ties, and a severe warning has been issued against those who sever them. The closest kin deserving of connection are parents, and the Quran and Sunnah have urged righteousness and kindness towards them. Therefore, the questioner and her mother must maintain ties with her father and be kind to him in every possible way, including visiting him if possible. The fact that he suffers from memory loss does not negate the obligation to maintain ties with him, be righteous towards him, and be kind to him; for this is an act of worship and a command from Allah Almighty, and it strengthens bonds and love, and fulfills the father's right.