Although optional, Synago’s planning algorithm supports your need for keeping some fixed days free and others booked. When doing weekly plans, Synago can attempt to avoid days you prefer to be left unbooked.
Different congregations can have different rules about who counts in a minyan. Synago supports both in-eligibile and eligible in order to encompass an entire congregations and the supporters, not just a select few.
It’s normal for members of one congregation to also visit other congregations in their vicinity. Synago supports optimizing for minyan on a larger scale, and can help two synagoges in close vicinity to share their members in order to optimize the chances of minyan.
We prefer it does not happen, but sometimes we’ve got to cancel on our promise to show up for minyan. Synago acknowledges this problem, and can silently attempt to mobilize other members of the congregations and save the minyan.