Getting stocks in UK into US brokerage

My wife used to live in the UK, and had family purchase stock for her as a child that has since been sitting in various different accounts. We are now, finally, trying to get that money out of the accounts, but they have said they require a CREST number for a US institution to take the stock. Because she is not UK-based, she also cannot sell the stock either.

None of the places we have tried — Fidelity, Vanguard, Merrill — have particularly understood what a CREST number is, and after escalating it to various managers have always gotten an answer saying they cannot do that. Is there any solution here? Is there a brokerage that would be able to receive these stocks so they can then be transfered to her brokerage?

Thanks for the help.