Is a father justified in beating the mother for not wearing the jilbab in front of her relatives? And what is the ruling on recurring family disputes and the consequent severance of kinship ties?

If you strike your father, this is a grave act of disobedience (uquq), and you must fear Allah and cease doing so. You should advise him gently and kindly if he is wronging your mother. Striking one's wife is permissible in certain circumstances with Sharia-compliant regulations. Abandoning prayer is disbelief if it is done out of denial, and a great sin if it is done out of negligence. Regarding your paternal aunts selling the apartment: if it was with your father's permission, then boycotting them is not permissible. If it was without his permission, then it is not permissible for them to do so, but a boycott is still not advisable. The furniture your father left with your maternal uncles is a trust; your father cannot demand its return from them; rather, he must retrieve it himself, and your uncles are not obligated to deliver it.