This was a really fun room for our family. We were a family of four (two parents, a 19 year old, and a 13 year old), and did this while on a sort of "vacation" in the Metroplex. We did this room with 4 of us, and I think that would be the minimum number you'd want, but I think it would accommodate up to 8 people. The detail in the room(s) was pretty elaborate. We were able to finish in time without too much trouble (we thought we were behind at first, but the last "half" went much faster for us).
We didn't know exactly what the theme would be beforehand (witches span a gamut from the occult to fairy tales); this was more of a "fairy tale" theme room than "witch" room (which was what we were hoping for), and I think it would be appropriate even with younger kids. Many of the puzzles had some aspect related to fairy tales in them, which we really enjoyed. Lots (though definitely not all) of the puzzles had a kind of "combination lock" aspect to them (i.e. do something to get a 4 digit code to unlock a lock), which might or not be to your taste.
We did this room after trying the Poe room in the Arlington location. Most of us liked the Poe room better, but our 13 year old preferred this one. But, they were both great rooms, and we'd certainly try another Secret Chambers room based on our experiences in these two.