Arras to Vimy for 5 passengers - taxi or rent a car?

Hello!
We are a family of 5 (2 adults, 3 children between the ages of 4-9) who will be renting an apartment in Paris from August 18-25. We want to spend a day at the Vimy Memorial site, and are planning on taking the train from Paris to Arras. We have read that a taxi ride from Arras to the memorial is approximately 25 euros each way, but we were wondering how difficult it is to find a taxi that will accommodate 5 passengers? Are we better off renting a car at the Arras train station and driving to the site ourselves?

Thanks in advance for your time/assistance!
:)