Mortgage lenders look for 35ish% debt to income. Some will go up to 45%. Even 50% sometimes.

The first one is very reasonable. The second two imo are borderline irresponsible.

Their rent payment doesn’t matter for getting a mortgage.

If they can’t get a mortgage; it’s either their income isn’t high enough to keep housing to an acceptable percentage or they have other debt issues.

That system isn’t the problem. That’s all very fair. Remember; just because they’re paying rent doesn’t really mean they can afford that rent. A lot of people are paying more rent than they should.

Which leads to the biggest issue being zoning and a lack of units leading to higher prices which have nothing to do with mortgages and is something they have a say in through voting.