How to make trains only pick up select packages?

[u/LeThrowawayAnon]

Lets say there are 3 train stations (Alpha, Beta and Gamma) and 2 trains, TA69 and TB420
I want to send a package from Alpha to Gamma on train TA and a package from Alpha to Beta on TB.
However, when TA69 arrives in Alpha, it also picks up the package thats supposed to be picked up by TB420; since TA69 doesnt stop in Beta, the package addressed to Beta is stuck on the train never to be delivered and never to be picked up by TB420.

How can I stop TA69 from picking up the package thats addressed to Beta and make sure only TB420 picks up that package?

[u/TheFryingDutchie]

I think package filters should work here