Private car from Prague to Krakow

The Ceske Drahy has an overnight train departing Krakow at 10:15p arriving in Prague at 6:12a. Although it doesn't run everynight, it's a great way to travel because you go to bed in Krakow and wake up in Prague. This way you don't waste a precious day traveling. The conductor will knock on your cabin door 30m before arrival and help you off. With a party of eight, you can share two couchettes. You can purchase tickets from the Ceske Drahy's website or RailEurope, although I read the latter is more expensive.
Ryanair also flys nonstop between the two cities with a flight departing at 12:30p.
If you hire a driver, you're talking about a 5h 30m drive, that's a long drive and expensive.

Many people don't sleep well at all on night trains, which severely compromises their functionality the next day. If they're so exhausted they need to sleep in the daytime, the result can be a bit akin to jetlag. (That has happened to me.) I think the odds that every member of a part of 8 would handle a night train well are virtually zero. I bet half the adults will say, "Never doing that again." I have a feeling children may do better.

These are the stops that night train makes after departing Krakow. How well will your light sleepers deal with experiencing braking, station noise, and acceleration 9 times between midnight and 6:14 AM?

Katowice 12:07 AM
Rybnik 12:52 AM
Chalupki 1:23 AM
Bohumin 3:28 AM
Ostrava 03:37 AM
Ostrava-Svinov 3:46 AM
Olomouc 4:46 AM
Ceska Trebova 5:36 AM
Pardubice 6:14 AM
Prague 7:56 AM

Those times are for trains departing tomorrow (Tuesday) night.

It's none of my business why the OP wants to take a private vs. the direct train (sorry, I can't recommend a private car) - because it's 7:44 train trip from Prague to Krakow during the day? Because it would take up a whole day of traveling? (instead of a night train?) Because they want to stop somewhere in between?

One train option instead of the long direct train might be a stopover in a town like Olomouc - take a morning train from Prague, stop in Olomouc for a few hours (leave the bags at the train station), explore the town, then take a late afternoon train on to Krakow. The late train probably requires a change in Katowice. So...that would breakup the train trip quite a bit.

Otherwise, I'd probably try to take the Ryan Air direct flight if it could be worked out. But as a lover of trains, I would probably enjoy the long direct train - not everyone would.

The OP asked about car transfers, not trains, so they most likely have a good reason for wanting to travel by car. It appears that mydaytrip.com will do a private transfer for eight people for 887 euros. I do not have experience with that particular company, so check their reviews. We did drive that route a few years ago, and it was a little over 5 hours, not 7:44. To me, that's a better solution than trekking 8 people to an airport, or trying to sleep on a night train. Have a great trip!

Yes, do use MyDaytrip. We highly recommend their service (used from Budapest to Ljubljana in spring 2019).