I agree if the kittens have been outdoors, they will want to continue that experience. It may be best to get a bengal who has been raised inside a home. I think you will be happy with any bengal. I say that because you've NEVER had a bengal before and you don't know what to expect. Expect surprises! Your bengal will not be like your parents' cats. I love your idea of expanding the space vertically because that is exactly what you bengal will want. I commend you for taking on the challenge and happy to know that you have family there who can assist you.

I am not sure how to share a video, but I was offered a kitten from one of the UK breeders I spoke to.
It is around 320£ more, so quite a lot. But it is younger (having been born the 27th of March), mum and dad are known for being really cuddly and sweet.
(I know the quality is not good, it was taken from a video)