Hanoi airport to Sapa via taxi

My wife and I will be arriving at night with a toddler and a senior citizen (70+).

The hotel quoted 8,500,000, which seems very high. Since we will be arriving at night and may want to take one or two short stops along the way, can someone recommend a private taxi provider that we can pre-book?

It seems that ordering Grab inside Hanoi airport isn’t easy. Can we trust 12Go Asia to pre-book a cab?