Shared calendar

Hello, I have a customer that has 7 users that need access to one shared calendar the problem I have is they don't use the same mail server part of the group have one domain using blue host and the other part of the group are using google apps with their domain email server. The requirements is really just posting events on the calendar, some users can use the web browser to access the calendar but 3 of them are using outlook 2016 and would like to access the calendar with outlook, they really don't require the events organizer to be listed on the event they just need to know of these events so I was thinking of setting up a free gmail account and give each user the password but my concerns are if anyone delete or add an event there is no way to know who setup the event, the group say this is not an issue, my other thought was if someone leaves the group we would have to change the password asap .....I am just not sure if this is the best fit, are there any other free solutions that would be better than this idea?