What operating systems? macOS?
For the record, Dropbox et al. are not backup services. Do not assume that something stored on a cloud sync service is backed up.
A backup should be a copy of your files stored away from your files. A good backup strategy might be to regularly copy your files to an external harddrive and less regularly to an offsite storage. I use a Keyboard Maestro macro for the former and Backblaze for the latter.