I got what you mean, there is no misunderstanding!
In order to do you requests, your site has to be multisite.
Responding to your questions:
1. Yes it responds to your requests, and you should have the multisite to do this.
2. It won’t affect anything for the customers, except the website URL will be http://www.jamhourendowment.org/fr for the french version. Each site(English & French) will have it’s own admin panel for editing it’s content separately, knowing that the content will be connected. You can read more about how wp-multisite works if you are interested.
3. Now you only have 1 site, so you decide either to be EN/FR.
The main problem at your site is that your server “windows server” refuses to be a multisite which prevents us from adding multilingual plugin, So what we propose is to contact your host support and ask them to activate the multisite from their end, we believe that this is the fastest solution