Hi Greg

Yes, you can use ProxyPass with or without SSL to forward external requests to internal webservers and the chosen SSL certificate does indeed get passed on. I use it for a couple of Servers and use Lets Encrypt Certs as well.
Its not that hard to configure and you should get the hang of it in about 10 to 15 minutes. Haven't tried it with multiple domains though but with Subdomains pointing to different internal servers it works just fine so i guess it would work with TLD's as well.

Things to remember when setting it up:

Target server: Depending on which Protocol you choose (http/https or both) you enter the corresponding http://internal-serverip or https://internal-serverip
Target path: If you want to simply point it to the internal servers main root folder you can leave it empty otherwise /foldername

The rest should be self explanatory

Hope this helps you out otherwise don't hesitate to ask