I like the direct approach. Since you're not that concerned with keeping good relations with the in-laws, it only makes it easier to say this with the right tone. The next time they make a thinly-veiled insult:

Your comments about my housekeeping are getting really tiresome...

If they start to look like they are not taking your seriously:

...no, really. I'm tried to be nice. I've tried to give you the benefit of a doubt that you're not making underhanded insults. But I'm at the point where I really can't take it any more.

Now put them on the spot for an answer:

Can I rely on your to stop making these sort of comments about my housekeeping?

At this point they are likely to back-peddle, and comment that they were only joking, etc. That's fine. But don't let them avoid the question:

That's all well and good. Thank you for telling me. Can I rely on you to stop insulting my housekeeping?

Repeat the last sentence as often as needed until they provide an answer that indicates they have taken you seriously.

I like the direct approach. Since you're not that concerned with keeping good relations with the in-laws, it only makes it easier to say this with the right tone. The next time they make a thinly-veiled insult:

Your comments about my housekeeping are getting really tiresome...

If they start to look like they are not taking you seriously:

...No, really. I've tried to be nice. I've tried to give you the benefit of the doubt that you're not making underhanded insults. But I'm at the point where I really can't take it any more.

Now put them on the spot for an answer:

Can I rely on you to stop making these sort of comments about my housekeeping?

At this point they are likely to backpedal and comment that they were only joking, etc. That's fine. But don't let them avoid the question:

That's all well and good. Thank you for telling me. Can I rely on you to stop insulting my housekeeping?

Repeat the last sentence as often as needed until they provide an answer that indicates they have taken you seriously.