Newly created time machine backups are huge

I just wiped my old Time Machine backups (desktop and laptop) on 2TB Time Capsule - both were over 500GB and Time Machine unable to restore files.

Wiped both sparsebundles

How did you do this? Did you use AirPort Utility to erase the Time Capsule disk? Did you use the Quick Erase or Zero Out Data erase option?

At the completion of the disk erase process, you should have had 1.9+ TB of free space on the Time Capsule drive. Did you verify this before you backed up the Macs again?

Do you have any hard drives connected to the Macs? If you do, then Time Machine may have backed up your Mac....and....the attached disks unless you specifically excluded the attached drives from backups. Is that a possibility?

Finally, if the Macs have been "upgraded" to Catalina 10.15.x, there have been any number of reports from users who are having difficulty with Time Machine, so that might be a possibility here as well.

It is not a new problem. We have reports of this happening going back several Mac versions. Time Machine can go mad. It seems to never end and creates long backups.. very seldom hear of it happening on two different Macs at the same time.

The situation is kinda strange now with latest APFS formats. You are showing Mojave as the OS in your profile but Catalina is the one that has the most issues.

Even if the desktop and MBPro are only showing 120GB of files that does not mean there are not hidden files on the disk which are not counted. If the first backup exceeds the actual drive capacity then you know things are really screwy.

We don't recommend Time Machine for use on network backups now. Honestly it is not sufficiently reliable.

I use Carbon Copy Cloner as most of us here do.. there are other alternatives but CCC is worth a look.

If you want to do Time Machine then a local disk plugged into USB of the computer is really the only reliable method.

Note people report success with Time Machine and Synology NAS. I do run Time Machine to Synology NAS which has been trouble free.. BUT I am way way back on 10.11 (El Capo) OS. I also run CCC to a local disk after bitter experience taught me Time Machine is not up to the task.

Recommend that you completely and securely erase the Time Capsule disk using the Zero Out Data option in AirPort Utility. The Quick Erase option has done some weird things in the past for me....and.....it is not a secure erase.

Finder is not all that great either, especially with a Time Capsule.