You have Thunderbird on an Android device? Really?

You can share a Lightning calendar by saving it as an ics file and then setting up a network calendar that links to the ics file. This is a share rather then synchronisation, because only one machine can "own" and access the file at any time. If two machines make their own copy and edit it, the second one will overwrite changes made by the first. Thunderbird's design assumes it is the sole user of a profile and the contents thereof, so locks its profile to ensure this. So there is no provision for managing concurrent changes made to a file by a third party

Store your ics file on a shared drive on your network, or use a tool such as Dropbox or Sharepoint to allow a device to grab its own copy of the shared file.

I run for myself, as an ongoing experiment, two non-google shared calendars. One is operated by an email provider, gmx, and connects to Lightning via caldav, and the other is an ics file on Dropbox. The latter works for me as I have computers in two locations (home and work) which never operate simultaneously.

OOPS! My bad.

I use email on my cell phone so rarely, I forgot that T-Bird wouldn't run on android. The email is a built in app (I'm assuming, as it doesn't id itself.) I just check the 'notify' to see what emails are waiting for me when I get back to my computer. (I hate smart phones because they are smarter than me, lol.)

I mainly want to sync my calendar, reminders, & contact's info on all 3 devices. If I copy the pertinent files from 1 device to a 2nd, I would lose the info already entered on the 2nd device. I want to merge data on all devices without duplicates or losing any info.

I think your idea of a shared folder with the appropriate files would work fine for the computers, but the cell phone is another thing. I really need to see my appointments and reminders on it when traveling, but I don't want to manually enter them because I might miss something or they might get changed. I also want to find a good mileage app for business trips.

FYI, cell phone is using 'Marshmellow', desktop is Vista HP 64bit, laptop is Win7 Pro 64 bit. I don't know anything about Linux, but some people have recommended 'Mint' to me, and I've been told that upgrading to 'Lollipop' would be a big mistake.

Am I stuck with google?