Wife's Grandma wants to sell her house

[Colton Witte]

My wife's grandma is wanting to move closer to family. Her house is located in a housing edition that is great for single family's or renting out to the local college students (the campus is within walking distance). She's asking a bit much for what the house is worth, but I can be ok with the price. I would like her to do a seller financed deal on her house and I get the conventional loan on the house she has up here and then she can rent that house. I believe that the rental can cover both the payments for the seller financed deal and the conventional. While it would be tight, my wife and I can support both rental payments if there isn't a renter in the one. I know this doesn't allow for major repairs or us making money. Our goal is to have heathy income stream once we retire. 

My father-in-law however does not like this proposal but doesn't have any explanation for why. I think he think's I'll be taking advantage of her, but I think it's a fair deal. Am I missing something?

[Colton Witte]

@Randall Alan, @Clayton Silva, @Bill B. I appreciate your replies! I truly am not trying to take advantage of her, I am trying to help make this situation a win-win for everyone involved. Not mentioned above was that she would live in the new house rent free and I would be responsible for the property upkeep. The value of her current house is less than the value of almost every house she's looked at in our area. 

I agree that the whole thing would be messy and convoluted. 

Again, I appreciate the feedback! I will just do the conventional loan for her house.