Driving into Germany over Easter weekend

This does not directly answer the precise question you have in mind, but provides a compromise between driving and flying. Especially if you think that flying (into Saarbrücken) is too expensive and if you do not wand to land in the middle of nowhere.

London - Saarbrücken can conveniently be done by train. Take a Eurostar to Paris Nord, walk to Paris Est and take a direct ICE or TGV train to Saarbrücken.

As an alternative, you can also travel by Eurostar from London to Brussels, then by train from Brussels to Luxembourg and finally by bus from Luxembourg to Saarbrücken. It is much slower slower, but might be a bit cheaper. Brussels-Luxembourg is 41 EUR return (and possibly less if you are under 26 years old). Luxembourg-Saarbrücken is 8 EUR one way.

Have a look at the DB website for the schedules. The Man in Seat61 has some advice on buying tickets.

I'm a bit suprised that nobody has mentioned it before: if you have never driven in another country before, it means you are only used to left-hand traffic and as your introduction to in right-hand traffic, you're planning a 9 or 12 hour trip.

That's seriously risky. I've switched from right to left hand, and while it's not a huge thing as such, it requires concentration. Which is going to be in short supply on such a long trip. Possible mitigation strategies (not necessarily mutually compatible):

• If one of the others is experienced in right-hand traffic, let them drive as much as possible
• Switch drivers so you don't get too tired
• Make several pauses
• Consider spending a night somewhere on the way
• Have everyone be alert for possible mistakes by the driver, especially at crossings and when making turns
• Get a good long night's sleep before you start the return trip, especially if you drink any alcohol at the party.

One of the things you need to take with you is a safety vest, it's required in Germany. For the kick of it would try to run without sat-nav, if you can afford to lose some time now and then. I wouldn't make the 9 hours of Google maps 12, it's normally quite accurate if you don't stop. So it's a full days drive, stop every 2 hours for 15 minutes (change the driver), eat and drink well.
Cheapo tip, go into Luxembourg, the fuel is cheaper than in Belgium, Germany

Under EU law all driving insurance covers you for up to 90 legal minimum insurance driving in any eu country.

So your UK driving insurance will cover you for 3rd party driving insurance by default. That's included in your premium. If you want to increase that (eg if you have fully comprehensive insurance in the UK and you want that on your trip) , you'll have to contact your insurance company and pay a little bit and tell them what countries you're going to. I think it cost me €50 in Ireland to get my regular insurance to cover me in loads of EU countries.

So there should be no border/insurance problems. Yay for EU.

Many cars in the UK do not have to EU flag licence plate. If your vehicle does, then you're fine to legally drive all over EU. If not you legally need to to put one of those GB round stickers on your vehicle. To be honest, this is highly unlikely to be a problem for you.

The link to google maps suggests another itinerary than described in the question. In any case, for this particular trip (UK to Saarbrücken), you should really consider the route through Belgium and Luxembourg (i.e. driving along the coast to Dunkirk/Dunkerque then heading towards Brussels and Luxembourg on the E411). You would be saving on tolls and have the opportunity to gas up in Luxembourg, saving perhaps 50 to 80 € on the whole trip. The distance is about the same and there is absolutely no point in avoiding Luxembourg (in fact people from the region actually make detours to go through the country and buy cheap petrol and cigarettes).

Beside the train and the car, flying to Luxembourg might also be an option (no idea about the price but it is really close to Saarbrücken).