OK, but why do you care about uniformity? If it’s just some OCD-adjacent urge - that’s fine; do what makes you happy.

But from a technical point of view, VLC will play back no matter what the codec and compression level.

The question is why do you want to convert them?

If you use something like JellyFin as your media server and client, it will transcode them as you watch them. If you’re on your phone using crappy WiFi, it will adapt the bitrate down automatically. If you’re at home using a projector connected by Ethernet, you’ll get the original file.

If you think you’re running out of space, it’s often easier and cheaper to buy more HDDs. H265 and modern audio codec will save you a maximum of 50%. For about £200 you can get a 15TB HDD.