Am I sinful if I do not open the door for my maternal uncle who knocks on our door repeatedly and annoyingly, at late hours, causing disturbance to my husband who needs rest?

You bear no sin for not opening your home to your maternal uncle and his children, fearing harm, due to the general evidence on averting harm. This is while being keen to maintain his affection and kinship through other means, given the great status of kinship and its maintenance, and because he is a neighbor who has three rights.