I’ll third Colp and Dkny’s suggestion of Saalbach. We went there this summer and had a great time.
The Joker card really is fantastic, free access to lots of things (lifts, water park, crazy golf) and discounts on lots of other things just for staying in certain accommodation (ropes course, go karting, quad bike, Segway). Lots of fun walks up the mountains with adventure trails and adventure playgrounds etc… Proper mountain walks if the girls like that too. Our apartment cost €600 for the week (price up how much a lift pass would be for most places), would accommodate four very comfortably, had secure bike storage, included Joker cards for each of us for the whole stay and was about 3 mins from the nearest lift/5 mins from town. Huts on the mountain do lovely food for a very reasonable price.
Zell is about 15 mins away by car or a bit longer for a very gentle ride.
Salzburg is about an hour away for a city day/sound of music tour.
The riding is excellent. You can make it easy or challenging by choosing different lines or routes. Plus you get an uplift per day for Leogang (although one of the trails linking Saalbach and Leogang is a rooty nightmare!).