wow, so much info provided within a single kit and crossover too.
mk6 GTI - has a CCBA or CCBC engine (EA888.1 engine)
mk6 ED35 - has a CDL engine (same engine as golf 6R)
dual temp level sensor?
I am taking you mean the car is showing low coolant? If so, check it's not low on coolant and waterpump is infact working
If verified - then replace coolant bottle. That is where the level sensor is located. when cold and right tools. Should only take approx 20-30 minutes to sort.
Can direct you to someone in chch if your require help
reading your post a few more times, I believe this to be your only issue and now you know how to sort it.