The answer you receive will vary based on which political ideology you ask.

I will answer from the perspective of an anarchist.

Your Aunt and her Husband are not committing the greatest of evils, but in the grand scheme of things, they’re a part of a bigger problem, one that they themselves would not even perceive, and in fact would have strong personal incentives not to grant legitimacy were it explained to them.

An anarchist, or libertarian socialist, are generally against the concept of private property in all forms. This is not to be confused with personal property, which are things you personally own and use, such as the house you live in, your car, your tools.

But private property is something you own to extract profit from simply by the act of owning it, and necessarily at the deprivation and exploitation of someone else.

Buy owning those townhomes that they themselves do not live in, they are able to exploit the absolute basic human requirement for shelter in an artificially restricted market, and thus acquire surplus value in a deal of unequal leverage.

You could argue they are justified due to offering below market rates, taking on the financial risk of owning and maintaining the property, and fronting the capital to own the investment.

But the issue is: their choice to become landlords is what in fact creates the conditions in which they can then offer solutions to in order to claim justification.

For if we consider if landlordism were completely abolished, and people were only allowed to own homes they personally use, it would result in an insane amount of housing stock to flood the market, causing housing prices to plummet. This would in turn allow millions of lower income people to be able to afford a home and pay it off quickly, allowing them to actually build wealth for the first time instead of most of it going to pay off rent (remember, your aunt charging below market is the exception, not the norm).

Most humans would much rather pay off a small mortgage on a non-inflated home themselves, instead of paying off someone else’s mortgage and then some.

But that’s all assuming we have a housing market still. In an ideal Anarchist society, housing would be a human right, and every human would have access to basic shelter and necessities of life, like was enacted for a short time in Catalonia during the Spanish Civil War.