Being an ally is inherently about making a commitment to become more conscious and behave with more integrity. Defining the characteristics of an "ally" is already difficult, and adding questions about membership in an allyship group makes things even more complicated. Some questions to ponder below as well as suggestions on moving forward.
Should members need to make some kind of pledge? Can a pledge be private or must it be public? Once they pledge, should they be held accountable in some way?
Having an official commitment pledge helps make clear to both aspiring allies and others in the community what allyship means in your context. Use both the existing commitments resources and also host a smaller version of the Town-hall brainstorm event in which folks in the Partner Group create their own list of allyship requests.
The upside of having the pledge be public is that it invites that person to be more accountable; the downside is that if people are publicly designated allies, but they don't act like it, the allyship program is greatly diminished (additionally, some people who otherwise might get involved with the program but who just are more introverted might decline).
Holding people accountable is very tricky. On one hand, if you don't hold people accountable then the pledge begins to be seen as worthless. On the other hand, you don't want to create a shadow-disciplinary committee and deciding who does and doesn't get stripped of an "ally" title is very tenuous ground.
All things considered, to start out, it's safest to have the pledge be private and to not have a formal process for holding men accountable – an informal invitation by men who sign the pledge to be held accountable can work, depending on office culture.
Should non-members be allowed to attend events and receive newsletters?
The aim of any allyship group is to bring in and educate more allies. While some events are designed for those with more understanding and dedication, effort should be made to include folks who want to learn more but aren't yet sold on signing a pledge.
Should we charge members dues? How else to finance allyship events and activities?
If your group doesn't have any funds, then you may want to ask the most committed men to pay dues to become official members (in addition to the commitment pledge). For the those who care somewhat about D&I and allyship but aren't going to pay money, they can still sign the commitment pledge. Get everyone you can to come to events and sign up for the newsletter – find ways to get people to chip in for food or other costs without that being a barrier to entry.
Should allyship members become part of the Parent Group? Should they pay fees?
You may want to ask dedicated allies and people on the leadership team to pay into and become members of the official Partner Group. Take the lead from your Partner Group. Don't let joining the Partner Group be a barrier to entry for guys who want to learn more!
Member value proposition
Defining membership of an allyship group is tricky. Members get value for joining, but it's a different value proposition than any other type of MBA club. The point of joining is not to enhance members' careers, provide members support, or offer members social activities (though those may be incidental outcomes). The point is to help enhance others' careers, help make the community more inclusive for everyone, and support peers who face challenges that members don't face. That being said, for those who want to become more inclusive leaders, these allyship groups provide great support and educational resources that the rest of the MBA experience don't necessarily provide.