lokesh soni I highly doubt a free tier server will support 25k users even if it only runs node. Putting node and nginx on the same server is fine nginx takes very little memory. MongoDB will try to use as much memory as possible so it should be on its own server. Unless your app is very low traffic with 25k users you will probably need 2-3 servers and they should be bigger than t2 micros.
Remember a t2.micro is like 1/4th the power of a modern cell phone. So 25k users running on part of a cell phone.
It's very much possible to do everything you said for a test environment, but never for a production ready app.
I believe you can run a t2.micro instance for close to 1 year for free (I may be wrong here, perhaps the terms have changed). Try looking at digital ocean, alibaba and google cloud as well. Most of them have free tiers too.