We think you'll need more than a lawyer because they don't cover the whole process:-
If one or either of you have been resident in the UK for more than seven years then the Estate and Gift Tax DTT will assign primary taxing rights to the UK, except for property and businesses in the US
http://uniset.ca/misc/us-uk1980.htmlThe first step is to work out likely tax on both estates, first and second death (that's four computations), then take into account any existing gifts, then consider whether either party is likely to go back to the USA at some time.
The second step is to consider tax reduction techniques. Lawyers usually use trusts - a by-pass trust is normal - planners think in terms of using assets that are exempt and insurance trusts, and also consider how your IRA pensions can be passed estate tax free.
The third step is to look at the next generation, what they need, and how skilled they are at managing money and then decide the strategies and the tactics.
Then we go to lawyers and often use Thomson Snell & Passmore.