You can do essentially anything that you want---------- as long as you have a "business purpose" for doing it.

That said........I would merely sit down with a spread sheet, and use columns for years, rows for the alternatives..........and begin plotting what could happen.

Map out what will happen under Alt A......from gross income down to taxable income, and the resulting taxes...........then Alt B, etc. etc.

Your mother might have a little more expenses due to depreciation on fences/tiling if she can be called a producer, but that also means she will have self employment income/taxes.  If buildings are involved.....then depr will increase.

The overall principal for her is to merely level out her income.

That means that for the "new" 2/3s that will now be rented, instead of farmed.........use the spreadsheet to level out the rental income so that it is no more than the prior earnings that she and your father had from farming.........and, give due consideration that her return will not have the SE tax that her/your dad's return had...........unless circumstances result in her being a "material participant" in the production process.

So.........merely level out the rental income, even if she takes a lower amount in the first few years.........and higher amounts in the later few.

Have the lease cover the needed years to accomplish all this.

BUT-------- and this is the key--------- have a "business reason" for varying the amounts of rent from the short amounts in the nearby years (with the real purpose being to level out her income) but with the STATED reason being....for example.... to assist a youngster to get established, with the consideration being the higher rent in the back years.......etc etc.

The reasons stated do not have to be perfectly logical------ they just have to be evidence that the parties gave due consideration to the problems, set forth solutions, and memorialized such in writing.

"Business purpose" is a big deal, especially in transactions between related parties.

You really need a good tax-orientated CPA involved------ and he does not have to be a "farm expert"--------- merely because your problem relates to any cash-basis transaction between related parties.......very common.  Might be unique to you, but it is not to the rest of the business world.

Final point........... remember that the self employment taxes kick in only if she were to be involved in the production process (see Section 1402)........AND only then on rent received on LAND.........not equipment, not buildings.  So, be creative.

Edit....a final-final point............. make sure the estate attorneys look real hard at how the land is titled.  In many cases, even though a spouse would have to sign in order to transfer or to mortgage, for state law purposes, the "ol man" kept things in his name.  If that were to be the case.........the entire parcel of land would go thru his estate return.  There would probably be no estate taxes, just because of the spousal exemptions........BUT your mother could easily receive a step-up in basis on the ENTIRE parcel (land and buildings, etc).......and not just "his half".

Do not "assume" your estate attorney.......or your accountant......... would catch that difference.......easy to overlook.