This sounds incredibly convoluted and problematic for you. Generally, any financing structure that is this unique is a turn-off to new investors, especially institutional investors. That they've recently raised funding for their business but are contemplating building a new business with you (as a subsidiary) is a concern unless this was part of the plan they articulated to their investors and investors are aware and supportive of this initiative. Finally, it seems as though you are being asked to invest a lot of energy in something that is entirely dependent on future funding validating the business, which is always a significant risk.

Obviously, I'm missing a lot of details and so happy to talk in a call but I would say based purely on how you have defined this situation, that it seems more trouble than it's worth to you.