It looks like you have two conflicting opinions there; one says prorate the expenses based on square footage and the other says, it's not deductible because the yard is not rented out.
I'm going to give you a 3rd and 4th opinion (3. you prorate by number of residents and 4. you don't have a rental, you only have roommates sharing expenses).
If this is merely a cost sharing arrangement where the amount paid is below fair market rental, there would be no reportable income to you. If the “rent” amount is fair market value, or more, there is still some question as to whether you even have to report it, as it almost always comes out zero. Most people take the attitude that it is not income; it's just room mates sharing expenses and ignore it. Family, as opposed to unrelated roommates, makes that position stronger.
Here’s what you may be required to do:
Report the income (enter at Rents & Royalties/Income & expenses from Rental Properties); and then deduct the expenses on schedule E. If the roommates has full run of the house and yard, and there's just the 3 of you, then two thirds of your expenses are deductible (mortgage interest, property taxes, insurance, utilities, repairs, and depreciation [if needed}). Your net income will usually be less than zero.
What you are NOT allowed to do, because it is your own home (you have "personal use") is claim a loss from this activity, to offset other income. Because of the "personal use rule", your deductions are limited to your income. Net effect ZERO.
It is possible for you to gain a positive tax effect from this activity; If enough of your schedule A deductions (mortgage interest & property tax) are shifted to Schedule E, and your standard deduction becomes bigger than your itemized deductions, you will have effectively saved on taxes.
If you have no mortgage (and mortgage interest to deduct), then there could well be profit involved, which you may have to offset with depreciation that could lead to "recapture" in the future when the property is sold.
