Transferring\Selling S-Corp shares between existing SH's

A client reached out with the following request, and I'm curious how others would respond.

Client is an S-Corp with two shareholders. A owns 51% and B own 49%. They recently told me they always intended the ownership to be a 50/50 split even though it was setup 51/49 (I'm unsure of the origin of this). To make the legal reality line up with their internal view of the business, they want to get to a true 50/50 ownership split without triggering any tax consequences for either SH. Currently the business has negative RE due to multiple years of losses, and as such, both SH have losses in excess of Basis.

I'm not sure there's any way around tax consequences for one\both SH's as I believe they need to establish a value for their stock and then recognize the gain\loss on that sale. Also, if they go the "gift" route my sense is they then are "rolling the dice" as that probably wouldn't hold up to IRS scrutiny if audited.

This is not to even mention the potential cost involved. It's my understanding that they should probably have a lawyer write up a stock transfer agreement, and then sign a consent form & get it notarized. I'm wondering if the fees (me, lawyer, notary, etc) are overkill for simply doing a 1% transfer to give them peace of mind.

Curious how others would approach this situation.