Check in my Windows 7 and Games thread. It seems to me I could not get the Myst Masterpiece Edition to play without a lot of tweaking. I finally downloaded the GOG version and even it needed something to get it to run properly. I believe they have fixed that by now though. They list is as working on both Windows 7 and Windows 8.
I don't have the Delaware St. John game to test on Windows 8.1.
I don't remember if the Agon games were listed in the Windows 7 thread, so check there. For the most part, if a game played in Windows 7, it also played in Windows 8.
What I do with these games is to first try to install them normally. 99% of the time, that works. If there are issues, the next step is to try compatibility mode. If that works, then you're good to go. If none of that works, then I install in Documents.
If your Myst is the original Myst, I doubt it will work natively in Windows 7, but it's worth a try.
GOG has the Myst games for $5.99.
Heading out to the gardens!