Thanks for all the quick replies, was expecting to have to wait a while! Will try and address them all.
We did used to have all our DVDs in French as well as a xmall collection of kids books in French. But I think it was around school age that he refused to watch them anymore. Likewise, he didn't want dh to read to him in French anymore. So dh started reading in English, we swapped French for English DVDs and that was that. We've tried a few times since to reintroduce, but he'd rather not watch/read anything than do it in French 
I am not comfortable speaking full time in French,as I said, and I was always under the impression that having chosen a method one should stick to it - we chose OPOL and so, imo, we stick to it. But it's not working as dh would like hence him wanting to change method. I'm not sure a few days a week of me speaking French is a particularly good idea - as well as which, when I've tried in the past to have a whole day in French, I always end up reverting back to English, because it feels wrong for me to speak French with my kids.
We've looked into after-school French clubs, and ds1's French is better than what we've come across. I think he'd be bored. We know two other francophone families: one the couple is French and desperately want their son to speak more English and the other who has a much older girl
. Neither seem to offer the right situation for a play together! There is a local French Saturday group, but dh dpesn't drive, so it would mean me taking the boys and again, English is bound to creep back in.
The long holidays with grandparents we had considered before, but dh is concerned - they are not particularly good with children, in spite of having 12 grandchildren, dh's dad is getting old and I think would find it hard. No point in even asking dh's siblings, they are mostly estranged apart from one brother who.... well, it just wouldn't work for the time being (that's a whole other thread though!)
Dh does spend time with the boys, but not an awful lot so as they'd actually have to talk! I could try and encourage him in that sense as well as encourage him to start reading in French again. We don't have a whole lot of money to be buying all new books in French - is it possible to get such things through the local library?
Bertie I think it is almost certianly a bit of this. I heard him a few weeks ago maintain a very respectable conversation in French with his mamie on skype, yet he never ever speaks like that with his dad. Any idea why they do this? Or ways around it?
Will def google l'Allian Francaise, thank you.