It would be nice if you could give us some idea of a budget. And approximate date.
The drive from Calgary to Great Falls is just 5.5 hours. Add an hour for a stop half-way (in Lethbridge) for lunch and you'll be here in 6.5 hours..
Helena is 1.5 hours from Great Falls (86 miles/ 140 km). You're on interstate all the way so you an make good time.
Generally speaking, there is little difference in price between hotels or motels in Great Falls or Helena.
The deciding factor for your will probably be how your family is feeling and if you and they want to push on after arriving in Great Falls or call it a day here.
Regardless, have a safe trip and enjoy Montana.