why dad's behavior has been changed suddenly and dramatically?

Gurri it sounds like he's losing it. Let's hear from the Psych Dept

A sudden change in behavior can often be a sign of a medical problem. Can you or your mother get your father to a doctor for a checkup?

Gru, Jes' suggestion pertinent tho hope we hear from some of our psych partis

I am afraid he will not listen to us and get extremely angry.....

Although it could be a medical condition, there's other possible causes, such as him not wanting to be married anymore, but doesn't want to be the one to initiate the divorce. Both the delusional claims, and the anger can be signs of this.

The reason that is a possible cause is because the behaviour started when you moved - which is very coincidental. This scenario iss much more likely if you were the last child to move out, or if you were the last male child to move out....but then again, severe stress can trigger mental conditions, and also, coincidences do happen, so it could be medical.

A way to help determine if he is just looking for a way out of his marriage - if he thinks your mother is his maid, this is delusional...people can't help delusions (if it's a medical condition), and there will be delusions in other areas of his life and conversation.

In the end, you need to sit down and talk with a professional, and give them all the information you can.

He's already angry. And it can get worse.

Plus, he would be nice to the doctor.

Does your mother have family who can intercede? I'm guessing not, but there may be sympathy if you explore that.

This is an odd comment from me, but do you have any friends in the police? or would they be on his side (whatever that is)?