For starters, I'd say a lttle bit of dirt never hurt anyone ... when we were younger we used to get filthy and my um wasn't a housekeeper either. We survived, and grew up with actually LESS health probs, I guess we built up immunities to it. Likewise we had no ac back in those days either. Now if you have reason to worry about mold, that could be a problem. I'm assuming she uses fans though. You can get like charcoal packages that absorb the damp and cut down on mold, I wonder if you could sort of broach that with your ex MIL, just as a worry, and give her some to place in each room while the girls are there?
As for the mosquitoes, that's another story, as they can carry quite a few nasty diseases, so I'd get a good no-DEET bug spray for your girls (or a sunscreen lotion that contains an anti-bug component) and just ask her to make sure and put it on them when they go outside. Does she have screens in her windows? If not, maybe you could ask your ex to do his mother a favor and put some in, I'm sure neither of them wants to see the girls bitten.
Sounds like you are making things work between the 3 of you, so I honestly think she'll respond ok to your concerns. And if you really are worried about hurting her feelings, just blame it on being a first time mom and maybe being overprotective of Kat and Kayla. You may end up with her giving you more advice but she'd feel needed and it would make your other requests seem less threatening.
Good luck!
Now,LOL, I am an AVON rep and my website is www.youravon.com/rosemarydempsey
and AVON really does have some of the best no-DEET bug stuff available. You can register and order directly from the site, the product line is BUG GUARD, and it comes in pump action or aerosol sprays, and the lotions are in flat tube-like containers. They are in the $4.99-$5.99 range right now, which is half the usual price. now if you do go there to get them, pick direct delivery and enter SHIP3 as the promotion code for shipping as it will get you $3 shipping no matter what size the order.
Take care
R.:)