@cfisher-sifadis , while it is not unusual to divide the income/gains/losses equally between the joint owners if they file MFS, it could create an issue if the tax information documents like 1099-B etc. are issued in both names but ONLE ONE SSN is used. Because the IRS income match program ( AURS) will see a mismatch and therefore issue a CP-2000. All you have to do is respond to the notice and explain that the income was recognized 50% by each MFS filer-- included copies of the relevant supporting documents. That should settle the issue.
Is there more I can do for you ?