Time Machine Compatibility with external drives

Hello apple community and thanks in advance for the help. I have a Mac Mini and I am running out of storage. In the past I have used Time Machine to try and recover Pics in a new codec that were not compatible with the the old hardware that I have. Since I have been using iCloud. I had about four points in time / backups to go back to and thought , ok, I'll start at the most recent one and see whats there, if it is not what Im looking for, I'll just go back further. The problem was that when I went back to the first, most recent backup, the Mac thought it was time for a backup at that point in time. So with "back-up-automatically" checked, it went ahead and backed up again without me catching it. It made another copy of the one I just went back to and overwrote the oldest one that I had. I made it halfway through my backups before I had accidentally deleted so many memories. Needless to say I don't want this to happen again and have since turned off the auto backups and am much more skeptical of this program. My question is, how can I use a 4Tb HHD for time machine and use a 1Tb HHD to store pics on in parallel with the drive built in? Can TimeMachine Backup a copy of multiple HHDs on one "TimeMachine Backup"?