Thanks everyone for your input and advice.

If its correct that (assuming we got green cards before the children were 21) the green cards for the children expire at 21 then there's a real worry as I wouldn't want split the family up.

I think I will have a look at the other forums.

As it is for the moment I will get my brother to also make some enquiries and in the meantime we look forward to our trip in Oct and our lovely car hired by UScarhire.