Constitution] because it handicaps duplex owners who occupy, forcing them to 'move or sell' (as you aptly noted--they can move out and take out an investment loan, or sell, both choices are burdensome.) 

Housing for Older PersonsThe Fair Housing Act (FHAct) protects all residents from discrimination on the basis of race, color, national origin, religion, sex, handicap or familial status (families with children under the age of 18 living with parents or legal guardians; pregnant women and people trying to get custody of children under 18).The "Housing for Older Persons" Exemption: The Fair Housing Act specifically exempts some senior housing facilities and communities from liability for familial status discrimination.

But every time I make a little success, it's as if I pull back after that and become handicapped for a while.

If you're born with a physical disability, a mental handicap, if you're born a minority, if you're born into poverty, etc, you are less likely to succeed than those who don't have these challenges.I'm not saying these people can't succeed (clearly they can), but it is much more difficult and much less likely.Just like if you and I were running a 50-yard dash against each other.

Each one is handicap/wheelchair accessible.

Kids, service dog, minority, handicap it makes no difference they still must pass screening criteria.

He said that this would most likely mean that we would have to put in an elevator so that the second floor is handicap accessible.

These dogs have attached an elderly lady and then a month later an elderly man, then trapped a handicapped man on his boat dock. 

Two stories aren't good unless you have a handicap accessible elevator.Group homes are often covered by state requirements, your division of health and welfare or similar agency.

AgeDisabilityEqual Pay/CompensationGenetic InformationHarassmentNational OriginPregnancyRace/ColorReligionRetaliationSexSexual Harassment Those are for employment and are not the same as as the fair housing act's protected classes which are:  race, color, national origin, religion, sex, familial status and handicap