Upvote:1
In most cases you will be able to get both boarding passes before you go:
Even if you complete the check-in online you will still have to go to the check-in counter to present your documents needed for an international flight. Depending on the airline and airport in particular, you can use a faster lane for those that have done the online check-in. For some combinations, the only thing that you get for checking in online is selecting your seat from the flight map.
It can also happen, although rarely, that you check-in online a confirmation that says you are checked-in but this is not a boarding pass, in which case you will have to get to the check-in counter to convert that into an actual boarding pass. This is usually to check-in your documents.
Upvote:2
If you bought your ticket with Aer Lingus as a single flight with a lay-over, it's possible that your second flight has a code share, and has different numbers (one flight number with Virgin's prefix, and one with Aer Lingus' prefix). If so, you can check in only on your first flight and receive both boarding passes.
If you deliberately bought two separate tickets for each leg of your trip, then you'll probably have to check-in again with Virgin Atlantic.
I experienced something similar in my travel GIG->AMS->CDG with KLM. I bought it as one ticket with a lay-over. The first check in on KLM's website gave me the two boarding passes (even though the second flight was an Air France flight (with the AF prefix code) it also had a KL prefix code. That's code sharing).
Upvote:5
If this is a single ticket/booking, you just check in with the first airline and in most cases you should get the boarding passes for both legs. There are exceptions though, so you should check upfront with the airline.
If these are two different tickets/reservation, than you need to check in with each airline individually (using both apps)
Keep in mind that some international flights do not offer online check-in since some airlines want to check your travel documents during the check in process.