That really depends on the horses and the saddle. If all horses are similar build and you have a good half pad to compensate minor fittingissues that can work for sure. But in the end, the horses decide whether they like the saddle or not.
Havery you tried a good qulaity memory foam half pad? They help ill fitting saddles...horses that are changing their shapes (building up or down ). They come in different thicknesses according to your needs.
As long as it fits yes but if not I wouldn't. I use my saddle on my 16.3hh warmblood and a 14.1hh paint and it fits both of them. I got it to fit my horse but my friend wanted me to ride her paint and my saddle just so happens to fit so I use mine.
Though if it doesn't fit or causes any pain I wouldn't use the same one
You could try getting a customized saddle and have it fit to the both. Even if they different builds. Don't know how this worked but my friend had a custom CWD made and she was able to have it fit to her narrow, high withered 15.3 standardbred and to her wide, 17.3 draft cross.