avoid another paid subscription.
It is a "subscription" in the sense that a calendar is being received from a sender. It's not like you are paying for a daily newspaper. You send your calendar, your husband receives it; he sends his calendar your receive that. It is part of iCloud and there is no charge.
should I delete our calendars and start over on all our devices?
If you have the detail of your events written down then that would make a lot of sense and start with a clean slate. Once you have uncoupled the tangle on every device as discussed above of course. Start with one Mac - I find it easier to work on my Mac rather than an iPhone with this sort of detail and I suspect you might also. I presume here that both of you have exclusive use of a device, or at least separate user accounts on the computers.
When you have entered your events into the calendar on the Mac follow Apple's instructions (previously linked) to share the calendar, by email for example - this means to publish your calendar and email the invitation to your husband to receive the calendar.
Then go over to your husband's Mac and receive the invitation there. As I recall when the invitation is accepted Safari then fires up to take you to iCloud on the web to sign in and to finish the acceptance, so have all the credentials prepared. iCloud calendars cogitates for a moment and adds the incoming calendar to the iCloud account and that should mark your success. Once that has happened all the other devices should automatically be synchronising (after a pause for them to digest all this) because they understand the status of the calendar settings. The last step is to do the same from your husband's calendar on his Mac and to send an invitation to you which will be received and accepted on your Mac.
The problem is my husband and I are in our late 70’s and only want to share 1 calendar each with only ourselves.
I don't see this as a problem! Well done for being fearless about interacting with the technology. My mother is late 80s and she does lots of things with her Mac. Most of her friends can't manage to pay a bill online and trot down the the post office once a fortnight to waste an hour of their day because they don't see the value in learning how to do it, or can't be bothered.
Late 70s or mid 20s like my daughters, it's all the same in getting these systems working for ourselves. That's why these forums are a great resource - Mac and iOS users around the world (I'm in Australia), from all walks of life and from different levels of experience sharing their experience and questions.
I hope this fixes your frustration.