Not my problem - I'm their manager. If I have 2000 engineers I just make one of them Lead Dev and then shout at him when he hasn't been able to deliver after I gave him 1999 software engineers. What an idiot.
Describe the app generally, and leave it to them to form their own teams and solutions. Hackthon style, and hackathons at least usually have functional prototypes by their end.
No way you can delegate work to 2k engineers and tell them what to do for next 2 days. Physically impossible.