If I install Morroblivion, can I still play normal Oblivion?
I have a stand-alone version of Oblivion and the Steam version of Morrowind. Can I install it okay despite this difference?
Also, if I install Morroblivion, can I still play the normal Oblivion game using saves in the game I've already made?
Thanks in advance.

You shouldn't have any
You shouldn't have any problem installing it, and you can still play Oblivion. If you use the transport mod that comes with it, you can play through Oblivion and Morroblivion on the same save. And if you use a mod like my ArmoryLab for Morroblivion ( https://www.nexusmods.com/oblivion/mods/49847/ ) you can go back and forth between Cyrodiil and Morrowind pretty easily.