Where in the world would you get 150 - 200k for brother 2. Even if you were correct that the value of the assets was $400k which I think is too high, then the maximum split three ways would be $133k. It is definitely going to be less than $400k because she would not have netted $180k on the house so probably more like $120k at best.
Taking into consideration that the trailor park and the house could have lost money over the years, it could be even less than that.
Don't get me wrong, I think that sis is morally in the wrong to some extent, but I think that the extent is probably significantly less than you imagine.
House was bought 70. Sold 180
Trailer park was bought 100. Worth around 160 today.
In my humble opinion, Brother 2 should have the lion share in all this, cause:
Son 1 already got around 70k
Daughter lived rent free + pocketed money destined to the family for years. ( estimation around 200k total)
So if everything worth 400 (or even 500) today:
Sis: 400/3 (minus rents pocketed from tenants + rents saved each month living for free) (To put to her credit all taxes and HOA and expenses she paid over the years, not quite close to what she saved by living rent free)
Bro 1: 400/3 (minus 70)
Bro 2: The rest.
That's what seems fair to me today and to the rest of my family.. All but her.