How to stop visits from friends with young children?

My husband and I are in our late 50's. We have friends in their (she is 35 he is 58) with 2 young children age 2 1/2 and 1 year olds. They come every other weekend without invitation and when you say you are busy they still come. The 2 year old is wild and jumps on furniture, throws things in the blink of an eye, waits until you are not looking then swats at vases, cuckoo clock whatever is in his sights. The parents think it is funny and actually laughed saying oh you should have seen your faces when he almost knocked over a $2000 flat screen tv we were trying to hang. I said it won't be funny if you have to buy us a new one and they just laughed. This happens every time that was just one example. We have worked hard for what we have it wasn't given to us! How do we stop them from coming? Our house is far from child proof. Our dogs (small 5 pounders) have to be closed in a room when they come for fear of them being hurt. (the dogs not the kids) This is so stressful. My husbands blood pressure soars when they come. We tried saying we would visit at their house but that doesn't work. They still keep coming. Clockwork every other weekend. We even tried hiding in the house but forgot to lock the front door and they walked in. We are past this stage in our lives of young children. Our grandchildren behave when they come yet these ones do not. We were only slight friends before they had children and now they act as if they are family. We have family and don't need this stress in our lives. Please please help. It is getting to the point we are going to have to say something mean to make them understand this isn't working out.