Freelander lost cooling water and went out all the time – Workshop wants 4000 Euro – Are you threatening to rip off here?

Hello, my parents have a little problem with their freelander. At some point the Freely didn’t start to lose any cooling water visibly. So after a few km of driving everything was cool water gone and the Freely went out. You had to tip back several times during the ride. In between there were phases there were a couple of days well, but now in the last days he went out every few meters and you had to tilt. In addition we noticed that a kind of “knock/kacker” comes out of the engine, and the oil z We tapped directly on the cylinder head gasket and brought the car to a workshop. They wanted to disassemble the engine immediately and look at it. Today we get the call that the piston valves have knocked out (or so similar), the cooling water in the engine disappears, therefore a replacement engine should enter, and we should adjust to 4000 euros !!!. Do you hold this for realistic or we will be pulled over the table. My father w should give already the OK for the Reperatur, however, I wanted to ask again here. Thank you already dear Julie