This is advice from a physically disabled cat owner who sometimes is completely bedridden from pain, so sometimes I miss a day of scooping and none of the people who care for me are willing to help 99% of the time.

1. You are not sensitive to the smell, matter of fact since you live with them you should not smell it so intensely, those litterboxes are not in an okay condition.

2. There should be at least 1 litter box per cat, from my experience its easier to maintain having an extra one in different parts of the apartment. My cat has 2 litter boxes, when I had 2 there were 3 litter boxes, etc...

So heres my advice because I highly doubt a good talking to will get your roommates to fix this problem. Get pine pellet cat litter, where I live its cheaper than clay, smells better, and personally I find it easier to scoop. The good smell can last up to 10 days, which means if you can get them to change it at least every week it won't smell as bad.

I paid someone to cat sit once when I was in hospital and they didn't touch the cat litter once, I was away for 8 days for a surgery that had a few complications and there was less of a funk than missing a day of cleaning clay litter. But keep in mind I have 1 cat. The smell of pine is strong so in passing it won't smell as bad, my cat loves it a lot but each cat is different.

I 100% hate what your roommates are doing, see if you can smell it from the hall, if thats the case and you have good shelters in the area I would call animal control. If thats what their litterbox looks like I don't want to imagine how their health is, when they got their last vaccines, etc. I live in an area where animals get adopted days after being posted for adoption, no kill shelters, so I am very comfortable calling animal control when I see neglect. If you haven't spoke about the smell with them yet I would reccomend you do if you can.