I dunno man. I'm an adoptive parent and didn't run into much of that. The visits from the fire marshal and health inspector ended up turning into expensive hassles but most of it came down to my wife and I wanting to become parents.

There are a lot of different types of adoption. International and domestic are hugely different.

International adoption is hugely different from country to country. Most countries have very different programs based on the age/health of the child and vastly different parental requirements.

Domestic adoption is hugely different from state to state and also can hugely vary depending on age/health of the child and whether or not you're going the foster to adopt route.

Things can get kind of weird/fucked up in a lot of ways. It sounds like your sister and her husband were trying to adopt a healthy white newborn baby domestically.

Those children are in the highest demand which makes adopting them super competitive (one of the fucked up things that happens). I don't think their getting turned down was the adoption agency or social workers doing.

It's more likely the parents giving the children up were choosing couples with higher income, other children, nicer homes, etc over them (also kinda fucked up but understandable).

I really don't believe anyone told them they had to give up because they were too old. If they were in their 60's or 70's age would be a problem. I know plenty of couples who have adopted children in their 40's and a few who have adopted in their 50's.

There are very few things that would completely eliminate adoption as an option for a person or couple, and they're all pretty extreme.