Use Family Sharing for just an iTunes account?
There are many people [including me] in this situation. Usually because the original iTunes account was set up before iCloud existed, so the email address is not an Apple address.  

This, in itself, doesn't make it any different to any other iCloud account &amp; you can treat them in the same way.

Set up Family Sharing on your current @me account &amp; set that as family organiser. Send an invite to the other @dot.com account as another adult, &amp; the same for the rest of your family [adult/child as appropriate]
Purchases will then be available to all members.

I have a recollection of, when trying to send the invite to my own @dot.com from @me, that the rescue/recovery address couldn't be the same, or the invite would never arrive. I remember having to temporarily juggle the addresses until I'd got it working, then change them back.