Our condolences for your loss.
It would be best for you to seek a tax professional in Wisconsin, a community property state. These questions would best be answered by a tax attorney who has more access to the related documentation.
In general, there is a step up in basis to fair market value at death. This can be either the date of death or 6 months after the date of death.
Yes, Form 8949, Part II, Box F should be checked.
Question 1-5: It would be easier to have the closing company issue corrected Forms 1099-S to each. Otherwise, it is acceptable to report Form 1099-S at your percentage rate.
Regarding reporting Form 1099-S, see: Where do I enter the sale of a second home, an inherited home, or land on my 2020 taxes?
Regarding Wisconsin law and the IRS, go to Internal Revenue Bulletin: 2004-30 and click IRS Revenue Ruling 2004-71 for other rules about splitting income between spouses in Wisconsin.
For more instructions, see:
IRS 2020 Instructions for Form 8949
IRS 2020 Instructions for Form 1099-S
You may wish to review this resource for more tax guidance about your situation: Death in the Family.
For full details, see IRS Resource: 2020 Publication 559: Survivors, Executors, and Administrators.
