Hi Elizabeth,
Yes, you can offer that kind of setup for your clients with the UltimateWB website builder. You can compare the 5 UltimateWB software versions and what features each has here: https://www.ultimatewb.com/compare-uwb . We have demos - the frontend and backend - that you can try out for each UltimateWB software version here: https://www.ultimatewb.com/demolinks .
Based on your project description, you will want the UltimateWB Full version for the members app and other social networking apps. This will give you an admin panel for the clients themselves. Please note that the backend in the demos is for the admin of the website.
You can try out the Full demos here:
Frontend: https://www.ultimatewb.com/demo/
Backend for admin: https://www.ultimatewb.com/demo/admin
Besides website builders, we do also offer web hosting and domain name registration: https://www.ultimatewb.com/domain-names-web-hosting .
Hope this helps! Please feel free to ask if you have any further questions.