Hi,

For this lot of blogs and writings are available in the internet. You can run the odoo 10 and odoo 12 in the same machine, for this you have to install both the python 2 and python 3. Odoo 10 is running in python 2.7 and odoo 12 is running in python 3. Once you install it, you have to create separate conf file for 10 and 12, as well as separate service.

Have a look at the below threads:

1. Install multiple Odoo instances on a single machine 

2. How to run odoo 10 and odoo 12 together in one system on ubuntu

Thanks

I would use docker for multi versions, so you can have odoo v10 and v12 by container.  

The beauty of this is even multiple odoo instances of the same version.  

I think postgresql v10 works fine for odoo v10 as well, so it goes like all odoo container depends on the same postgresql container.  

All instances use different ports, so you can interact with them in the browser.  

All instances share the same addon directory and as well a individual directory.