Talk to some realtors about what they have to say regarding resale. On 3 acres you shouldn't be real bad off if they are nice double wides around. I sometimes see that building lots in the most exclusive neighborhoods don't really cost that much more than some of the others and the cost to build is the same either way.
It is your nickle, do what you want. Values will be based more on square footage. Hope it isn't a mistake living near your sister but the same house in another neighborhood could be worth more. Most people think their brothers in law are bums. Why don't you build a house and snob hill and let your sister move up there?
By the way, if you see a rusted corrugated tin roofed tar paper sided trailer in that trailer park, then hello neighbor. lol