A big puzzle (for me)

I have a tab application containing several applications filling several tables with similar (sub)keys. Data about conversation, competences etc.

Now I have a grid / form with editable grid which I will link to this container. Select a conversation and jump to the application containing the data. I cannot create a link field due to the fact that the control app does not have a keyfield. Similar issue with Container app. How can I achieve such a thing?