They may be ok with staying with in-laws now, but when it happens, and your parents seem kind of overbearing (no offense), you’ll be in for a world of tug and war with both parties. Yeah renting seems like a waste, but it may save your (and your potential wife’s) sanity. Just some food for thought. There’s also a sense of freedom to not have to answer to your parents (or someone else’s) after taking such a big step (ie marriage). JMO but I was living alone before marriage.
The debt/marriage thing… if it’s school debt (ie, doctor, lawyer, etc) you better believe that they’ll be earning way more eventually to pay it off and have more than enough left over to live comfortably. But the debt thing is tricky because you really have to love the person to take on that burden in the beginning.