how to get base chart.yaml version from sub charts
I don't think you can access the .Chart of the superchart, anywhere, anyhow. After all, the subcharts are supposed to still be able to work as stand-alone.
The best you can do with helm 2 is to put the version in the .Values.global section.
In helm 2, you have to write it to the top-level values.yaml in the script that generates the version, because you can't have any code there. I believe in helm 3 it should be possible to generate values by script.
You can simply define version values for the subcharts in the values.yaml file inside the main chart.
In my view there is no point to create multiple subchart with the same version, you can simply run them as ordinary charts. The main goal of Umbrella charts is to deploy more/large scale application with a lots of params - more often different. So if your subcharts have similar params like for eg. the same version, try to deploy them separately.
Useful documentation: subcharts, charts-subcharts.
Useful article: helm.