AIBU to expect a cleaner family bathroom when staying with in-laws?

Couldn’t bear it. You make sure bathrooms are guest-ready. Go to a hotel. Sounds vile

It doesn't really sound unhygienic. Wet towels are normal in bathrooms and sanitary towel wrappers are just paper, though not scenic. I'd spend five minutes tidying up and put some handwash there if there's no soap or equivalent.

As a house guest would bring my own towel and toiletries.

And what was the problem about the laundry basket being in the bathroom? ..

This wouldn't bother me at all. It doesn't sound dirty, just messy. It's not a hotel.

You say no handwash. Was there a bar of soap?
If it were me I would politely ask PILs if there are any towels you could use and some soap/handwash. I would kick any clothes on the floor into the corner, and the fact there are clothes on top of the laundry basket isn't really a problem for you.
Yes, she's messy. It's not the end of the world. Suck it up for the few days you are there.

‘Have you got any spare hand soap for the bathroom please’

Your husband should clean, and then tell SIL to keep it that way and not leave her stuff on the floor.

It’s not your job!

I would expect your husband to tell his sister to tidy up her mess, but he should be able to find a towel?

Some people are dirty and messy, I wouldn't let my own kids living like this, maybe the in-laws don't care.

If you were me, what would you do (or not do)?
I would do nothing, not my house, very rude of me to comment. If I really hated it, I would stay elsewhere

I presume the parents have an en-suite and the sister typically has what would normally be the main bathroom to herself.

No need to complain just use your voice and say ‘ is there any soap for the bathroom? And could we have some towels please?’
simple.

I wouldn't clean it.

I'd leave it as I find it, and provide my own soap, towels etc. (keep your stuff in your room and take it in with you).

I absolutely would not stay there again - you say staying elsewhere "is not an option" - well, it IS. You're just choosing to stay there and put up with it.

Well buy some?

She's just used to being messy. As you say buy a cheap hand wash, shove her clothes in the wash basket and put the towel on a radiator. Lead by example!

She has a tendency to react defensively to feedback

How often are you giving her "feedback" to have noticed this is a pattern? And why?

It depends on how often they have guests I think. One or other member of my family stays at mine so often, that I’ve way past the stage of leaving a clean towel just for them folded on the bed and a chocolate on their pillow. None of those things are that bad, the handwash is a bit weird but you could have just plonked the shower gel you bought down to use and grabbed a towel from wherever they’re stored.

We’ve had people come and afterwards I realised there was no towel or hand wash. It just happens sometimes!!!

Why would the washing basket need emptying? That's where washing belongs. The washing on the floor should go in the basket.

I mean for me this would depend on the wider situation.

pils are elderly and have many illnesses and one is close to death and SIL is caring for them as best she can - shut up and sort it out yourself.

pil are totally healthy and SIL is fine - get a towel, get some soap (btw did you mean no soap at all? Lots of families use soap not habdwash) and have quite word

Are you going to use it or another bathroom?

How close are your family to his family? Is this a situation where you're all close and all muck in like he's still living at his parent's house or is this a more formal "visit" and you are the "guests"? If so who is doing the "hosting" in the house? Why isn't it his parent's responsibility to make sure the guests needs are met?

Either DH needs to sort it like he would have when he lived there, by mucking in or complaining to mummy. Or if that's not possible in his family dynamics, leave. Either go home early or find a hotel as your finances allow. I wouldn't stay somewhere with a messy shared bathroom without soap or towels. Get it fixed or leave

When I have guests, I always leave clean towels (bath and hand) on their bed for them. The rest of it sounds messy rather than dirty imo. I wonder if your MIL realises, given that they don't use that bathroom?

SIL sounds like a slob though. I hate cleaning and tidying, but my bathroom is always presentable!

Why is it "her" bathroom if it is the only bathroom in the house ? Fwiw yes it should be tidy but as it is her brother she probably didn't think she needed to bother.

If you were me, what would you do (or not do)?

Just ask for some handwash and a towel, or get DH to do so as it’s his family.

You could put the wrappers in a bin.

Leave the clothes where they are unless they’re in the way, in which case move to near the laundry basket.

Don’t say anything to SIL or PIL about it being messy!

I’d definitely have tidied the bathroom before guests personally and would be a bit surprised she hadn’t, but everyone is different and you can’t do anything about that.

How old is DS? It’s her home not an hotel and you’re invading it! If she’s kind enough to let you share her bathroom, you should at least be polite about it.

Ask your DH to speak to his parents about obtaining some hand soap/shower gel etc.

(cross posted with OP)