Is it legal to sell a house and have a total different picture in the ad "showing another house in the same neighborhood" instead?

NO. If your ad says the picture is your house, that is bait and switch as well as false advertising. However, if you clearly say the picture isn't the house for sale and is another house in the neighborhood, that's ok, but probably won't help you sell your house. Buyers want to see the property/house that's for sale.

No. Because any normal person is going to look at and inside the actual house that is for sale before making an offer.

No one is going to buy a house based on an ad picture.

Yes, thats called marketing. If it states the house in the photo is the one for sale, that is deceptive advertising but still legal.

Trade description,

Whats the point unless you want to waste peoples time and money

I don't believe it is illegal but i wouldn't suggest it. That would be false marketing.