Power BI would be my first choice for the dashboards. It is designed for reporting, charts, drill-downs, and sharing dashboards with people off site. You can connect it to an Access database, although for a shared multiuser setup I would strongly consider eventually moving the back end to SQL Server.

Smartsheet is more of a collaborative spreadsheet/project-management tool. It can be useful for tracking tasks, volunteers, events, and simple lists, but I would not use it as a replacement for a properly designed Access database just to get dashboards. You would likely end up duplicating data and creating synchronization headaches.

The important question is whether they only need to view data remotely, or whether they need to enter and update data remotely too. Power BI is excellent for viewing and analyzing data, but it is not a general-purpose data-entry interface. For remote updates, you could look at a web front end, Power Apps, or possibly remote access to the existing Access application, depending on the number of users and budget.

For now, I would keep the Access split database, build Power BI dashboards against the data, and make sure the database is backed up and maintained properly. Then plan the remote data-entry piece separately.

I've had making some videos with Power BI dashboards on my to-do list for a few years now. The list is so long... so long... I need clones.