If they’re MFJ this year they’re both your clients. The retirement monies are likely marital assets and how to handle the tax consequence should be done by agreement... or let the lawyers fight it out.
if you don’t have agreement of both parties, your setting yourself up for future aggravation
I generally take the position that the objective is for the IRS to (legally) get the least amount of tax and whack up the burden fairly.
If at first you don’t succeed…..find a workaround
