What do you think "market prices" would look like if every rental property suddenly went on sale and was no longer allowed to be rented out? Throw in some reasonable restrictions on what percentage of a region's housing any given individual or corporation can own so you don't get them all being bought up by development megacorps, and yes, most renters could afford to buy a property comparable to the one they were renting in. Heck, any renter that can afford their rent can afford to own the place they're renting even without crashing the market. If they couldn't, their landlord couldn't make money.
The service that landlords provide is to take on the risk of home ownership so that those without the necessary capital to cover unexpected expenses can live somewhere without having to worry about becoming homeless over a roof leak. Landlords provide insurance, not housing. On a long-term basis, though, the premium landlords charge exceeds the capital needed to have that security (since otherwise they wouldn't make money), so it's not a matter of the tenants being unable to afford those costs. It's a matter of the landlords being able to afford them first and turning a profit by exploiting those that weren't lucky enough to be born a few years earlier (both in terms of seizing the opportunity and in terms of taking advantage of lower prices when they bought).
Alternatively, sell it as three condos (or a triplex, or whatever you want to call it). That's going to require some regulatory changes, certainly, but the "problem" of so many houses being too large for single families can be solved without permanently keeping them as rental units. It just takes some actual will to do so from the government, who's rather enamoured with all the lobbying money they get from real estate investors and is therefore pretty keen on maintaining the status quo for as long as they can.
still too much for people with little/no savings to pay for. people can't even pay their rent right now, how can they afford a down payment plus monthly mortgage? You'd need to take down prices A LOT (i.e., have it tax-funded) for most people to actually be able to afford buying. If that's the solution you are proposing...good luck with that.