Fintech Startup organized as “subsidiary” of small consulting company

A mate of mine from university recently asked me to join his fintech startup as a fourth co-founder. After some discussion around the idea and market, we initiated the equity negotiation.

During the course of my due diligence, I came across a few -- shall we say -- oddities. The startup was being marketed to potential investors, partners, and prospective customers as a subsidiary of a small-ish consulting company wholly owned by my mate's father. That company's customer base overlaps with the startup's target market, so my mate framed the relationship as benefitting market recognition. Weird, but not disqualifying.

I of course review the cap table and quickly realise the father owns a majority stake in the startup as well.

I didn't immediately raise any concerns, but put the negotiation on ice while seeking more information. I listened in on a few of the investor calls and quickly gather that the father is positioning his consulting company to be purchased in tandem with any seed funding for the startup.

I confront my mate about it and he reiterates that the relationship between the two companies is just "marketing." How shady is this and what can I do to protect myself from this type of behaviour? Is there some document I should have drafted and signed to delineate the two companies? To be clear, the consulting company does not directly own shares in the startup, so there is not a formalised parent-subsidiary relationship. However the father's behaviour is worrisome because it complicates funding conversations (at best), and at worst could eventually lead to some sort of equity dilution or bait-and-switch that results in the consulting company being purchased, but not the startup. This is a bizarre spot to be in because I like the idea, the market space, and other co-founders.

Am I thinking about this the right way? Should I steer clear? What can I do to protect myself? Please let me know your thoughts!