French inheritance law is substantially different to UK Law. We advise that before buying your property in France, you seek advice at the earliest opportunity.
English Wills are valid in France, however producing one to a French Notaire following the death of a loved one would inevitably result in complications. There would be a requirement for the Notaire to obtain a legalised translation and certification as to its validity and effect. France does not recognise trusts either and since English Wills inevitably contain trusts, this again can lead to confusion if your estate involves French property.
Some of the options for structuring your estate are simply not possible to implement once you have bought the property. Therefore the earlier you seek advice the better.
You may be able to buy jointly (en indivision or en tontine). Or it might be suitable to complete a change of matrimonial regime possibly to adopt a communauté universelle, through a société civile immobilière or other form of company structure.