I have installed both Oracle Forms 10g DS and Oracle Forms 11g on same OS (windows) and same machine. At first I install 10g DS and it run then I install 11g in the same machine. After install of 11g whenever I running FMB in forms 10g at runtime it is displaying blank page in the browser and in 11g at runtime it is running fine.
my database is Oracle 19c
Why would you be installing two old and no longer supported versions?
Regardless, it is technically possible to install multiple version. However, I do not recommend doing this if you are not very familiar with the operating system on which you install them. Understanding, for example on Windows how system variables and the system Registry play a role in how applications work will help you to have a more successful experience.
Regarding the "blank screen", this is more likely the fact that you are trying to run an application in a browser that does not support Java any longer. In order to run a form you need to have a 32bit JRE (version 8) installed AND be using a browser that supports the Java plugin, which currently is only Internet Explorer and/or MS Edge with IE-Mode.
In Forms 12+ this limitation goes away because v12 introduces new ways in which you can launch your applications. Java is still needed, but there is no longer a dependency on IE.
More information about Forms and specifically the latest version (12.2.1) can be found on the Oracle Forms product page.
https://www.oracle.com/application-development/technologies/forms/forms.html
A great place to get Forms related technical questions answered and/or share your product comments is on the Oracle Community Forum.
https://community.oracle.com/tech/developers/categories/forms