I've just had enough

[Babywasinacorner]

Me and my dh blended our family about 6 years ago now and it's been good a few ups and downs but nothing major. We've gotten on, been a successful blend.
Anyway this all seems to be going tits up now and I don't know how to resolve it. His kids are 18, 14 12 . I had a dd who is 10 and we have a dd together who is 2.
It mainly stems from his kids being filthy, and I mean gross. I walk in the loo and there is shit on the seat, they use the loo for a poo and don't flush or wipe they just leave it there.. they don't wash their hands, don't keep clean and I'm just past being able to cope ( my sd 12 leaves used sanitary pads on her drawers. There is bin and bags to put them in in the bathroom) This isn't one offs . It happens every time they are here (50/50 split) I'm not a clean freak . My house isn't a show home but 🤢.

We've lost consoles/ phones/ been grounded when this happens as its always never them can't work out who it is ( it only happens when they are here so not my dds ), but it still happens . We go through basic hygiene, provide cleaning wipes, baby wipes . Im struggling to cope with trying to keep on top of their normal teenage mess and then this.
It's causing so many issues between me and my dh as we have them 50% of the time and we seem to spend all that time arguing about them..

Any advice please..what would you do??

They are angry and doing it on purpose. I hear you. We've had similar issues. All I can guess is that if your situation is anything like mine there may have been times in the past where the adults have argued about the children's behaviour and they know it. We sat our children down and had a calm conversation letting them know we argue sometimes but that's marriage. We love eachother and them but there are acceptable and unacceptable standards. Then as a united couple we put them to work around the house for a whole day, made them work and sweat to learn that keeping a home is hard work. They actually enjoyed it. If they leave messes we don't clean up after them. We just politely say "you need to clean up the mess left behind now please." Not later, now. If they refuse consequences are issued. So long as hubby and I keep on the same page and implement consequences together they realise this is a war they are not going to win. It's when we disagree or get angry with the kids that the wheels fall off. Then we are back to square one - bad behaviour etc. They break you. It's discipline in my view equally from both parents but so much easier said than done. Especially as we are a blended family with ADHD in the mix, it's tough. Put the little naughties to work I say! I sympathise and hope you and hubby can stick together on some points of change, one at a time.

My sd has been a little like this at times, and every single time she is called back to the bathroom and made to clean it herself. Every single time. It's better now but I call her out on it and I don't care who it's front of. She's also a young adult so know better too