2000 Ford Windstar front brakes

Two months ago vehicle seemed "hard to move" - smelled something burning & then smoke started billowing out from underneath engine. Melted plastic wheel cover on right front. Replaced front brakes and master cylinder and this lasted awhile.

Then it started again. Feels like I'm trying to drive in park; won't move. Again brakes heated up, after cooling down, I can drive it again for short distance. Took it in to a diff. Mechanic and he replaced brakes all around plus switch (as I couldn't get it out of park after starting to move into gear). Also all of brakes lights then worked (none worked before).

The next night it heated up again - same problem. Smelling burning smell. What on earth is this problem? I've called different places and they have come up with different remedies (some are just extreme I believe). Ford dealer won't talk to me on phone - have to bring it in. Have already spent about $500. HELP