Distance by road is around 620 kms, which as has been said, could take easily 7 hours, and follow the routes already suggested.

Entry into Qatar depends on your passport. I didn't need a visa beforehand for weekend visit, got one on arrival and paid 100QR at the airport ( UK Passport ).

Obviously, they will need exit / re-entry visa for KSA. Are they coming for a holiday or permanently?

Good Luck