Who is my son’s next of kin

If there is no will then both his parents would inherit equally i wpuld assume?

He’s not unwell but he really does not lead a healthy lifestyle. Sometimes I worry for his future, he has had a history of depression and binge drinking to the point that he has lost a job because of it in the past. Though he does hold down a very well paid job now that he seems to enjoy and is driven by it. Also, he lives off takeaways unless of course someone else is cooking for him (like me, every Sunday, to help make sure he gets at least one decent meal a week!

I actually think he’d rather any inheritance he may have to give in the future he would rather go to his step siblings children. I must now talk to him about this. He isn’t married or in a long term relationship or has any children of his own

Assuming your son isn't married, the house would be inherited by whomever your son named in his will, even if that was the donkey sanctuary. If he doesn't make a will then I believe you and your ex DH would both be classed as next of kin and the proceeds split. You could however contest it but it's a lengthy and expensive process and far from guaranteed. Far easier to just make a will in your favour. It's easy to do.

He does need to make his wishes clear with a will. Otherwise your ex could make things very difficult should your son pre-decease you.

Stating the obvious - your Adult Son really should have a will, especially as he will soon be a home owner. Do you know who he has nominated to receive his pension should the worst happen?

His parents until he has a legal partner.

If your son dies without a will, the estate would be distributed according to the rules of intestacy. It's a bit more complicated than what you say. It will differ depending on where he lives, e.g. the rules are different in England and Scotland.

www.gov.uk/inherits-someone-dies-without-will

If he doesn't have a long term partner, you are his next of kin
is he unwell?