WordPress Multi-Site: is it right for me

I've built a couple WordPress sites in the past, but I’ve never had to use the multi site (network sites) function in WordPress before and I am unsure if it is the solution I need.

I am essentially building two separate but related websites (possibly three). I’ll start with the possible third website. Which is for a 501 c3 (non profit), that site would just have a few public facing pages giving an overview of the foundation, any board meeting minutes, and ways for any donors to donate. So all public pages.

Next is a CERT site CERT is a Community Emergency Response Team which is a FEMA endorsed team of volunteers that might go out after a disaster and provide some basic first aid and help in triage of victims and aide local first responders (Fire and EMS). This site has public pages telling the general public who they are and what they do. It also has a member’s area where members can see any upcoming training, download forms/documents, and even a small forum for light communications. The last is a SAR (search and rescue) site that has its own public facing pages describing all of the SAR functionality. It also has a member’s area which should show the CERT members area stuff as well as extra stuff. All SAR members are CERT members but not all CERT members are SAR members.

Will multi-site allow me to have three distinctly different public facing sites showing the proper information and themed accordingly while allowing me to share pages and access from the members areas? I can obviously create one forums and allow or disallow user access based on roles using bbPress and something like Ultimate Member, but it would be nice to be able to have distinct themes while sharing data so as not to duplicate some things.

(what I mean by theme is that each site would have its own domain and logos, and colors. )