Is it obligatory to obey one's mother regarding not destroying paintings that contain animate beings and that were gifted before repentance, and does the validity of repentance depend on destroying these paintings?

You must advise your mother about the impermissibility of pictures of animate beings. If she responds, then that is good and a blessing. If she does not respond, then there is no blame upon you, and your repentance does not depend on the response of others. If it is possible to destroy these paintings without causing a significant harm, such as your mother's intense anger, then destroying them is obligatory. Otherwise, you are not required to do so.