UK life insurance with US benefactor (and custody of kids?)

We're trying to get some life insurance set up to make sure the kids will be provided for in event of something happening to DH and I at the same time. But in an ideal world, we'd want my sister - who's in the USA - to get the kids. How would that work both custody and financially to receive the money from the policy? Or should we set up a UK based executor that could deal with transferring the money to my sister in the US?

Can you tell I have no clue how these things work?!