Our home is very different to their mothers. At her house they had mobile phones at 6 with no restrictions, Xbox, switch and tablet all in the same year. In my home kids don’t get a phone until they are in secondary school an there are more boundaries so to speak.
dh is a great step dad but when it comes to doing actual parenting he struggles.
He never follows through on consequences to behaviour.
He actually told sc if their behaviour didn’t improve they wouldn’t be able to come here any more and they would have less time with him
This is the issue.
Look at it from their point of view. They come to visit dad, and are in a house with no tech toys, bored, with boundaries that they don't like.
DH fails to spend enough quality time with them to make up for the loss of tech entertainment (an almost impossible task given how tech destroys motivation, enjoyment, and attention spans).
DH is inconsistent in parenting, makes empty threats, and now the result is they get two nights a week at a hotel.
I am sure the hotel is great fun - what a novelty for children. Is breakfast included? A full buffet? Even better. And they get dad all to themselves, going on outings and fun trips.
Do they get to bring their tech toys to the hotel?
I can't see any way back from this.
Unfortunately you have married a man who is not good at parenting, and who has children from a very different home background.
(Children can learn to adapt to two very different homes with different rules and expectations, but it takes a lot of consistent work from the adults in each home to make it clear "this house, these rules" and not back down.)
Your mental health is a separate issue. You cannot and should not lean too heavily on DH to support you in this - you have to deal with it yourself.
Would you actually feel happier if you and DH permanently split homes?
You can carry on the relationship, just have two homes. Then his DC don't need to be in your home. Then in a decade or so when they leave home, you and DH can move back in together.
The cost of a hotel two nights every week must be not far off the cost of him renting another home for himself and his DC.