Don't have step children, but something that my DH is pretty obsessed with is our inheritance. Macabre as fuck, but that's another thread.
A relative elderly in her years has changed her will, it was that GC would get 'x' and then DC would get half of what's left. It's now half goes to each DC, they distribute as they want.
Seeing as GGC are now involved it was going to get messy, so it seemed the fairest option.
I've seen threads before where you have DH & DW who have grown up children, the will is written and OP is hopping because why should SS/SB get any of DM/DDad's money.
The best way I saw was that assets are split as seen by the couple. So DDad could leave so much to a remaining spouse, (bearing in mind they will have agreed assets and each persons share of property prior to death) then shares of capital to DC. Say a property is involved, DC don't get their portion until SM has passed away or sells. I hope this makes sense.
So say DDad had savings of £100'000 plus a 50% stake in a property. The money and the stake in the property is split according to what DDad stipulated in will. To make it easy, Dad has 2 children and a wife, the wife gets 1/2 of his share and the children get 1/4 of the property. So a cash sum of say £33'000, plus 1/8 of a property. You may thank, that's unfair as SMum has 1 child who gets more than you, but I'd say not all SMum's are evil, they may leave a provision for you to inherit a more equal share, say a further 1/8, so then you have 1/4 of the property upon death. Step sibling gets 1/2 of the property and whatever else.
Or another example, DDad has £100'000, 50% of that goes to SMum, 25% to each of you, then you hold 25% in shares of the property, which you receive upon death of SMum or sale of the property. In the same scenario they could see you as all equal in the property, he trusts SMum not to change the will, I don't know if she can legally, maybe a condition is written in that upon the death of SMum all 3 children get 1/3 of the property. Or you and your sibling are entitled to 2/3. The final 1/3 is for SMum to do as she wishes. I think it could be appealed though if SSibling is arsey.
I prefer to think people aren't such vultures and go with the deceased persons wishes.
I don't know much about it, but a relative has 3 children of their own and 2 step children. At the end of it all there will be 1 property plus joint savings. So it would be interesting to know how that's going to work. But input has been equal by both parties, all children are treated the same as we speak.
Imagine how convoluted it could get if say SMum remarries or cohabits after the death of her spouse. More step children are bought into the equation. I'm guessing for a probate lawyer that is a field day. Definitely a nice hot holiday somewhere exclusive after all that work. I would say in that circumstance you want to ensure assets such as property is split with your children upon death, so they're guaranteed a sum.