really don't get what's in it for the women
Well no, me neither, but that's where the radicalisation element comes in. Remember how the doctor said she would go and recruit more women to come by persuading them over the internet. The guys were then pictured doing the same thing and making life in the IS sound idyllic (free food, free accommodation, etc).
All the characters are given their own motivations. The doctor is clearly an ideologist who wants to serve the jihadi cause through medicine. The other woman is young, from a sheltered and rather spoilt background and she thought it would be romantic to be married to a mujahadeen. The guy with the beard thought he was following in his brother's glorious footsteps, until he found out he'd been beheaded as a deserter. The other guy, who became a suicide bomber last night, clearly just wanted to go and fight and be a jihadi and he didn't mind having a Yazidi sex slave either.