Jmeter: control the number of requests happening at one time

I'm doing performance testing on an app that does transactions. I have 25 threads but only 5 unique IDs.

Here's my problem: To avoid concurrency issue, I want to limit the number of requests being made during a buy/sell transaction to only 5 (cuz only 5 unique IDs). How do I achieve this in Jmeter?

Please be detailed in answer as i'm a total noobie. Thank you!!