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I think yes you can get away without the other servers and roles as you are trying to deploy a app and only for handful of users, basically you can install the RDS session host server and licensing on the same server or on the Domain Controller if you are short of resources and design your solution.
The Remote Desktop Session Host (RD Session Host) holds the session-based apps and desktops you share with users. Users get to these desktops and apps through one of the Remote Desktop clients that run on Windows, MacOS, iOS, and Android.You can organize desktops and apps into one or more RD Session Host servers, called "collections." You can customize these collections for specific groups of users .
In short the other server roles are:
- Remote Desktop Web Access (RD Web Access) lets users access desktops and applications through a web portal and launches them through the device's native Microsoft Remote Desktop client application
- Remote Desktop Gateway (RD Gateway) grants users on public networks access to Windows desktops and applications .
- Activated Remote Desktop Licensing (RD Licensing) servers let users connect to the RD Session Host servers hosting the tenant's desktops and apps.
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