There are not any national programs for this problem that I am aware of and you have to be very careful in offering different rent structures to different tenants. It can be a form of discrimination.
On the human side, we have found that it is easier to increase rents in family parks as they typically are able to afford it better (they just need to reallocate what they spend on). In parks with people on fixed incomes they may not be able to reallocate and that can be a problem.
It all boils down to the value you are offering as compared to the other types of housing out there. As long as you lot rent is 50% or less of a 2 bedroom apartment you should be ok but this is not a cut and dry formula.
If you purchased the park based on the rent increase and it is justified then although it is hard to listen to stories, it is business. If you want to gift the elderly that are having a hard time some money that may be a way around it.