Is it permissible to go to the mosque to seek knowledge while leaving the mother or sister alone at home?

Congregational prayer is obligatory for healthy men, and no one is permitted to forbid it, nor is there any obedience to anyone in disobedience to the Creator. One is excused from not performing it due to a valid reason, such as fear of an oppressor, or guarding Muslims and their property. Leaving one's mother or sister alone at home is not an excuse unless there is a strong presumption that harm will befall them. As for attending study circles, if your absence causes hardship to your mother, then prioritize honoring her. Try to attend the circles at other times or take them with you.