Not really sure what the "they're no Radfords" comment means.
I can't even understand why they want this many children, they're outsourcing the entire parenting experience from conception so it's not even like they just love having children and being parents. If that was the case they'd have one (maybe multiples if that's what the pregnancy resulted in) at a time and focus on raising that child at least through its new born stage before having another.
I can't figure out the motivation but I am sure it's not a good one.
I am against surrogacy in general, but the way this couple is going about it is absolutely abhorrent and I can't see how they can morally justify it to themselves.