Well, your Mini and MBA are both compatible with macOS Sequoia so I see no reason why you should not upgrade both to macOS 15.3.1
As usual we always advise a full Time Machine backup of your device/s prior to any Major macOS Upgrade.
Secondly, you should read up on the differences between the the two OS's. Here is a
reasonable article on the differences between Sonoma and Sequoia, just ignore the advert for "warp terminal" at the beginning:
Sonoma vs Sequoia. Compare macOS Sonoma to Sequoia. New features in macOS Sequoia. Should you update from Sonoma to Sequoia?
mac.install.guide
The major differences are the increased focus on AI, Stage Manager, Apple's new Password Manager (Useful), iPhone Mirroring (Never use it) and Windows Tiling.
Things to consider are other devices you may have and
their compatibility with Sequoia.