Easy way to have non-tech users modify database?
If you run SQL Server Enterprise edition it comes bundled with Master Data Services which sounds like it would do what you want. It was originally intended to merge multiple sets of data and come out with a golden master but if you think about it that process can be applied to almost any data work.

It's non-cloud so safe for internal use. It has a web application used to define and edit the schema and relations, and also for users to view/enter/edit existing data (they can also do the latter through an Excel add-on which is pretty cool).

Using the same web app you can also set rudimentary business rules about data checking, set up data export options (views), and there are other options for initially loading data using T-SQL. 

Data changes have lineage information and can be held back until approved by someone authorized. So there's a little workflow component possible, though I haven't seen that in use much.

For schema changes, it has some versioning/lineage capability, but I'm not 100% sure if you can see who made the change and/or if you can separate doing the change to the model from authorising a deployment of it. It has granular security, and it has a Metadata model to retain this information, but Microsoft have been on/off about whether they're deprecating that future or not.