@Toh Thanks for posting in our Q&A.
For Q1: Yes. We can upload these apps as line-of-business apps to intune.
https://video2.skills-academy.com/en-us/mem/intune/apps/apps-add#determine-the-type-of-app-for-your-solution
For Q2: I didn't find any official article stating that. So under my understanding, if the inhouse app is successfully installed on the device, the inhouse app can be deployed as line-of-business app via intune.
For Q3: For Android and iOS devices, we can refer to the following articles:
https://video2.skills-academy.com/en-us/mem/intune/apps/lob-apps-android
https://video2.skills-academy.com/en-us/mem/intune/apps/lob-apps-ios
Hope the above information will help.
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