Group of six friends, mums, jobs, busy lives.
You put this in the OP, so I'd agree with @Discointhekitchen , in the 2nd reply, and then so many of the other posters who are saying - you just have to go with it, or you'll never get to go out. As long as it isn't always the same person that misses out, you just have to accept at this time of your lives you are never going to get 6 friends who all work and who all have dc, and all of whom have busy live, to all have the same free dates.
Of course, all the way through, you then are saying "they could meet the following week" , which seems somewhat at odds from what you put in the opening post, potentially as you aren't been told you are right?
So, in this fluke of a situation, if it is true, everyone can meet together within the next fortnight, then yes, of course it would be nice to meet with everyone there but , as a general question, going back to your op, then, realistically, you are not going to get 6 busy mums who all work outside the home as well as their family commitments and other things in their lives to all be free on the same date with short notice very often, unless you all blank out every Thursday from now to the end of time, so it is a set weekly date.