Your entire story sounds like a red flag but the biggest red flag is that I don't hear a single mention of your users. Why are you asking "idea guys" for validation, you should be talking directly to users no matter what stage of development you are in.
From what you wrote, I really don't think you should take a cash infusion when the money runs out, just move on and find better partners in the future.
Note to other software engineers being approached by random angel investors: If you are being approached by an angel investor, please please vet them to make sure they are willing to do work. Ideas are valued at ZERO. If they are not technical, ask them to make a no code demo -- literally anyone can do this.