That was my assumption as well and I would likely need to be sure and communicate to the seller that they would be in second position with the lien. 

Here are my assumptions:FixedProperty tax - 2% of assessed home valueInsurance - $600-800 a year for SFRProperty management - 10% of monthly rent + lease up fee of 0.5-1 month of rentVariable 10% of monthly rent for maintenance 10% capex (depends on a lot of factors, so just an estimate)10% maintenance/repairs since houses tend to be a bit older.How do these assumptions compare against your experience?

Am I correct in these assumptions?

You could talk to the mortgage company about her doing an assumption in the loan.

This is significant, because initially, my brother & I were under the assumption that there would be some sort of nostalgia/sentiment for the house, since this was my great grandmother's house and my grandmother & Aunt grew up in the house.

My assumption is that the auctions go pretty high too.

If you're going to bridge the gap with financing:1) It would have to be 15+ years term on a 30 year amortization2) It would have to be 10% or so down-payment to spike the cash-on-cash return.3) It would have to be 0% interest year one, 1% year two, 2% year three, 3% year four and 4% year five through fifteen4) It would have to have no pre-payment penaltyAnd you would HAVE to make sure that you can cover the payments monthly with room to spare based on your assumptions of increasing rent levels.

The assumption made is that although you are paying a premium today, it will be worth much more tomorrow. 

Now this is an assumption but it seems like he may not want to hold those properties long term if that is the case if he does a portfolio refinance now he has to sell those properties together. 

When I put together revenue analysis for potential buyers and realtors in my area, I use adjusted paid occupancy percentages for my assumptions which takes those unpaid holds into consideration as to not overstate the revenue potential.