What are the limits of filial piety towards one's mother, and does it entail absolute obedience to her, especially if she interferes in all her children's affairs, embarrasses them, and diminishes their personalities?

Kindness to one's mother and obedience to her are obligatory, as long as it does not involve disobedience to Allah. Allah commanded companionship with parents in a good manner. The Prophet made the mother most deserving of good companionship three times, then the father, and clarified that parents are either the paradise or the hellfire of their children, and that Allah's pleasure is in the parents' pleasure and His displeasure is in their displeasure. Therefore, the questioner and his siblings must be patient with their mother and show her kindness, seeking Allah's pleasure and His Paradise, especially since she may not intend to embarrass him but rather to advise him.