As above – talk to the companies and tell them what you want. AQR will split groups if there are different abilities. Doug has a policy of not mixing groups of people unless they’ve been before and he knows their riding.
Weather’s not a certainty anywhere, especially once you get into the mountains. We’ve had some impressive downpours in Luchon in mid-summer (and when a storm comes in you want to be off the hills – I remember Matt Hart doing a massive descent and few miles on road on a flat back tyre to get home ahead of a storm).
Doug’s bit of the Basque coast gets a *lot* of rain but if it’s wet you ride on the other side of the hills (and the other trails dry quickly). If you want really dry you need to go beyond Europe – not much rain in South Africa in their summer…..