I went to Marrakech on my hen party (sounds an odd choice, but I wanted to be absolutely sure there would be no naffness!).
We were a group of 8 and had a great time - we all love shopping and culture, so it was easy to fill our time and please everyone.
Drinking was fine in our riad, we didn't go crazy but didn't have any problems. We also enjoyed cocktails and wine in restaurants, so while not sozzled, we weren't exactly sober!
It's not really a bar kind of place, and as a group of women we did attract some attention in the main square in the evenings, but nothing scary or uncomfortable, mainly just people trying to sell us crap!
We dressed modestly, but were OK in t-shirts and loose-ish/cropped trousers or dresses. You wouldn't walk around in shorts and a bikini top. In our riad we were happyily sunbathing in bikinis though with no issues at all.
I frequently travel to the Middle East and found Marrakech pretty relaxed if you're just out and about, but you're really immersed in the culture so are aware that you need to be respectful.
If you want a really relaxed stay, a riad is a great place to stay - you'll experience more of the culture (try one in the Kasbah, about a 10-15min walk from the main square.
Otherwise there are some lovely, more formal hotels in both the old and new parts of the city.
If your friends all want a boozy weekend, maybe do Marrakech with DH, if they're happy not to get legless, give it a whirl (and make sure you have room in your cases for your shopping!).