When trying to connect states, it needs updated version for Companion (current 1.5.6 on PC). Will the newer version of Companion be compatible with my older tablet with the MobileSheets app (ver 4.1.7)?
Yes, it's compatible. In fact, the developers provide a link to the old version of MobileSheets. You can find this message on their Companion page. It's right under the official download.
Companion page: http://www.zubersoft.com/mobilesheets/companion.html
It says: "Click here if you need the companion app for the original MobileSheets".