How to install two LMs in one ETS project and use them for different purposes

[Daniel]

I still think your problem is on the TP side. Your proposal makes no sense even for your application. If you want you can connect second LM just on IP side and disconnect from TP and use it as the API communication. LM to LM will talk over KNX IP.
What I wrote earlier is still the best solution, to divide this project in smaller ones where one LM will be enough to maintain KNX and your API.
Make sure that your cloud is not writing constantly to KNX as this will kill KNX and LM.