Is one sinful if one removes the receiver from one's family to prevent them from watching what displeases Allah, and one's mother becomes angry, knowing that one's brother provided an alternative for his mother, and should one prevent him from buying another alternative?

Praise be to Allah for your repentance before death, and you were right to prevent your family from using the device due to the danger it poses to their religion. This is among the greatest acts of righteousness towards your mother. Strive to advise them gently and kindly, warning them of the consequences of using the device for disobedience. This is more likely to lead to their acceptance.