It's up to the group, as a group, to set the rules. If all the other members are letting one guy decide the rules and going along with them, then they are still, in effect, setting the rules as a group. If a member of the group has an objection to one of the rules, he can speak up and try to sway the rest of the group to his side.
But this change, if it indeed does get accepted by the group, has to be agreed to before it goes into effect. So this one couple can't just break the rule because they've decided they don't like it. The husband either has to convince the rest of the group to change the rule (at which time, the wife can then choose to stay at home during the meetings) or he can drop out or he can stay in and abide by the rule (and the wife has to vacate).