Any suggestions for such a free App that runs on Android that will allow you to navigate the route?
That's tricky (and can be divisive!
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If you want to take a long term approach to getting a handle on digital mapping, route planning and navigation then you can't go too far wrong with Osmand. BUT (and a big but!) it is not the easiest to master. The downside is that it can seem complicated, the upside is that there are layers and layers of features that can greatly enhance bike adventures. It is especially comforting in that it works offline (once maps have been downloaded).
The good news is that for simple importation of a route and navigation of that route it should be very straightforward. It may even be free (you only need to pay if you download above a certain number of maps).
Navigation can be simply follow a line on a screen or voice prompts. Ir can also do route correction if you go off course.
However, whatever option you choose, I'd strongly urge you to get familiar with it well before you leave and to stress test it. By that I mean go off course, switch off data & wifi, change your destination on the fly and any scenario you can likely see yourself facing. Far, far better to do that on familiar roads than foreign ones. A good excuse to get out on the bike!
One problem is that some features are free and some are paid
This is something that applies across a lot of apps and is something that can change over time. It does not just apply to RWGPS. It can be a real nuisance when what worked for this week's tour won't work for next month's one because the payment structure has changed.
Another thing that is common across apps is that the format can be different to the website. Therefore if you always plan your route on a computer you may find it more difficult to do on the road on a phone or tablet.
The recommendation of RWGPS is a good one too. It has (I believe) the ability to record your ride and then allow you to add photos and comments as a real momento of the day. I do similar using Strava and this has become invaluable to me. Osmand will allow you to record a ride too, although the subsequent transfer to Strava/RWGPS is a tad more complicated, depending on your "tech head".
One other thing to remember if using a phone to navigate is that battery is important! Screens that are always on can really use up the battery. If using the phone normally too for photos, calls, internet you may find yourself without battery and unable to call or having to choose between navigation and keeping some juice in case of emergency. If nothing else it can add some anxiety where none is necessary. Pack a powerbank.
Also, the times when you may wish to make a detour (think pouring rain) are the worst times for trying to use a phone.
Finally, there is always the risk of a fall and breaking the phone - no navigation and no way to call for help, although as a group that risk is less.
As it happens, it's 5 years ago today since I was in Ieper...... so here's some inspiration
Ieper/Ypres
And the German Cemetery on the way to Ieper from Brugge, one of the saddest places I have ever come across
... but you can dowload other people's shared routes from RWGPS ... even if you are logged out and are using no account at all. For example: 
