Hey @E.Isaac1,
No worries. Let me see if I can make this more clear.
Megascans in Unreal Engine game → OK
Redistributing Megascans in Unreal Engine Marketplace Product → Hard No
Including Megascans in Demo Video for the assets so long as there is a disclaimer stating they are not included in the UEMP product → OK
Your Models must include their own textures and materials. They can not be sold without them. Any and all CC-0 assets (textures, materials, etc.) you use must be cited and linked in your description as well.
Additionally, you are free to create your own foliage assets and include those in your Arch Vis products and can use them again in your other products (with disclaimer). If you do so, you should still meet the content requirement using new assets, not the demo foliage from the previous product.
For uses outside of the UEMP you would look here: Epic Content | EULA - Unreal Engine