To end marriage due to step children

Still end up at the same place don't we? The kids not being all that interested isn't justification for spending so much time and money on stuff that actively excludes them. It's not remotely reasonable to go all or nothing with an expensive hobby and them blame the teenagers they barely see as it is. The adults must be the ones compromising and making the effort!

Also this. At some point DH has to parent and not pretend to have been outsmarted by a child for an easy life.

bring up every time. Correct it every time. He doesn’t need to be chatty be basic manners expected. You don’t get to be rude to people when you are in a bad mood. And if you are you apologise and self correct. It’s DHs role to teach him how to behave and become a decent adult.

Why? The OPs son is happy with regular lessons, he doesn't want his own horse because he doesn't want the slog of looking after horses in winter. Fair enough.
The SD isn't really interested in riding or she'd take up her Dad's offer of lessons. She's tagging along to events and is being dazzled by all the jazz - but all that takes years of hard slog and she's not interested in that.
I wouldn't be downgrading my competition horse to one a total beginner could ride either.

Those poor kids. Parents should be the ones hanging around and helping the kids with the kids' hobbies, not the other way around.

And how would you stop him ignoring her? What would be the carrot and/or stick?

Agree. It sounds like the riding isn’t really an issue here - with more info about the SS’s hobby of racing it seems like the father does spend some time with him alone doing what he likes. But OP is considering leaving the marriage because DH isn’t standing up for her as she’d like, yet the 13 year old boy has no choice but to live with adults he doesn’t know and perhaps doesn’t feel comfortable with.

You want to leave the marriage because you don’t feel comfortable in your own home EOW plus the other occasions they come.

When do they have the opportunity to feel comfortable in their own home? They have to deal with you at their dad’s and they have to deal with him at their mum’s. One of the joys with just having to deal with your own parents is that you can just relax and don’t have to live up to a set of standards set by someone who doesn’t love you.

This doesn’t really fly though. Our competition ponies are on a yard just like this, however I could buy a kick along cob and pay livery for it - and while it would be a bit out of place, nobody would stop me. So you could resolve it but obviously that would cost a chunk of money, which you don’t seem to be prepared to spend on her.

Another mystery hobby

It does sound a bit shit for everybody.

You would not be unreasonable to leave if this really cant be sorted. It's a shame if you and your H really love eachother but God, teens are hard enough when they're your own, can't imagine what it would be like to take this from other teens.

Could you move out but not split up?

I wonder how civil you would be if you were taken from your family and made to live with a random person.

The issue here is that his patents are not co-parenting.

it’s ridiculous. He has two parents they should be communicating about his behaviour. How is he at his mums has she noticed his behaviour ?

can there be consistent consequences or can she have a chat and vice versa. Would he benefit from chatting to a professional. Would he benefit from them all chatting with a professional together??

yes the relationship ended but there doesn’t need to be radio silence between his two parents when he clearly is acting up

I'm confused... if you have the children all together EOW (yours and step kids) where is your son while you are at the yard all day Sat?

I think you would be doing these poor kids a favour if you ended the marriage.

Also - how long has DSS been spending all Sundays racing, and was DSD involved in the decision that she wouldn't be able to see her Dad on a Sunday any more?

Its never going to be easy. Your dh isnt even a part time dad. It sounds like he has hardly lived with them let alone seen them on a daily basis. So relationships are always going to be strained.
Is all weekend every weekend about the horses ?
They probably take any frustration about him out on you . And blame you.

How long ago did you buy the horses and start spending all Sat there?

OP, you said here that “my son is at his dads when step children at with their mum”.
Does that mean your own son only joins you and your DH EOW as well?
I’m not judging, just trying to work out the dynamic, as (like others have pointed out) if your own son is with your DH more than his own kids are then that could understandably lead to them feeling resentful towards their dad.

If you read the OP's posts, that's not at all the case - she actively encourages time 1:1 with his dad, welcomes him into her home, despite his appalling treatment of her & he gets on well with her son. Obviously, he's probably not enjoying his living situation, but that's absolutely not OP's fault & she's simply asking for some basic level of respectful communication - that's all. He doesn't get to be appallingly rude just because his parents split up.

Leave if you want to. If you want to stay, that's fine too. It is what it is.

This all seems very insular. If I understand right DSS spends all Sunday with his Dad (each week or alternatively). So DSD never sees her Dad on a Sunday.

DSD spends some Sat mornings at the yard helping muck out the horses. Which is your hobby not hers. She can't join in there and then with riding. If she doesn't want to do the horse care she cant see her dad all weekend.

Meanwhile what is DSS doing on the Sat? Presumably entirety left out?

The whole setup seems really isolating for all the children.

As long as the couples are loved up that's all that matters eh?

She is a parent, she has a child too. Why are you being (wrongly) obtuse?
Two horses, neither of which any of the children can use. What sense does that make? They don't need to buy each child a horse, just common sense would dictate that one of the family horses should be suitable for the 3 children.
This all or nothing attitude is really weird and unique to horsey people and I feel sorry for the kids dragged along for the ride with little consideration.

I don’t give a about what people think

You said parents to refer to OP and her DH. She is not DSC’s parent.

And OPs child can't ride her horse either, so yes it is her job too.

OP has said her son does not want the commitment of caring for one especially in winter.