If you are getting all F’s, you are reading the pull-up resistor, not the DS18B20, I think. Are you sure the CRC is correct? Lots of libraries read the CRC but you have to turn on the part where you check the CRC.
Some people have had better luck using a 2.2k or 1k pull-up to +5V but you need to use a 5V tolerant pin.
There is a Dallas (now Maxim) document that talks about one-wire on long wires and your wires definitely long! They recommend using an active pull-down element (MOSFET) with slew-rate control. This limits the ringing in the long wires and makes the network more reliable. They also show a slew-rate limiting RC filter that you could try.
https://www.maximintegrated.com/en/app-notes/index.mvp/id/148
You might have a much easier time figuring out how to make this work if you could borrow and oscilloscope.