Need Help ASAP - Mechanics please

Hello, I was driving my 2009 Ford Flex to the mall on Christmas Eve when it felt like my car was pulling a bit when I was driving. If I took my foot off the gas, it would stop by itself without any use of the breaks. Also, I could smell burning when I stopped. I got to the mall and made sure the e brake wasn’t on so it wasn’t that. I called my brother in law who knows a lot about cars and he said it sounded like one of my calipers had seized. I brought the car to a shop
Today and told them what happened and they told me
That while they were checking they noticed two different fluids in my brake reservoir and said that all 4 of my wheels were seized. Which honestly didn’t make sense to me because I DROVE my car to them and the wheels were turning. Definitely having troubles but not totally seized. There was a strong burning smell by the time I got there I might add. They asked me if I could have added oil to my brake reservoir but it’s not possible. I may be a chick but I can read labels and the only fluids I topped up recently was my washer fluid and my power steering fluid because I have a slight leak but those reservoirs are both on the opposite side of the engine and I have topped them up several times so I know where the fluids are supposed to go. Now they are telling me they are going to have to fix the entire system and quoting me at $3500 to $4000...... I feel like I’m being taken advantage of and I don’t have that kind of money. A lot of other forums I have read the people say that if oil was in the brake reservoir it would make the brake system mush and not seize it up. Can this be something else?? I might also ad that my traction control and abs light comes on and off randomly for the last few months and I was told it was just the sensor. Any insight would seriously help me I just moved to the area from 3 hours away so finding a mechanic I can trust seems really hard.
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Complete flush of the system, a new caliper if one is needed, all new pads at a quality expensive shop, I would expect to be around $500. Use the internet to see what customers say about the other shops in the area and try one of them.
ABS sensor problems need to be tracked when the light is on usually. I have had Fords with a cracked sensor that would trigger the light when water got inside and go off when they would dry out. The big problem was having it stay tripped until I got a reading to find out which one it was.

If you're still having this problem, have you gotten out of the car and put your hand over each wheel while the problem is happening to see if one is much warmer than the other? I don't know much about late models and what all of the other system components are, but that sounds like a high quote. If one caliper is locking up, replace that one. You'll have to replace the pads on that end of the car, both sides, to make things even, and probably have those two rotors resurfaced and maybe new brake fluid but that should be it.

Nice Comet, '65Comet! I had early Falcons for years.