Answer to: Siblings buying grandparents' home as first time buyers. Please help me identify our blind spots

At current interest rates, an ARM would be ~$3k with tax/ins and similar rentals in our area get $3300-$3500/mo. Adjustable Rate Mortgages are by nature adjustable and very high risk. They typically have a lower introductory rate to compensate for the increased risk, but this means as soon as that ARM gets its first adjustment the introductory rate will go away and cause the monthly payment to jump up. This combined with the up keep costs of the house can easily outpace the rental costs in your area.