My husbands mother died 9 years ago and sadly recently his step father has also passed away. The stepfather left the entire estate to my husband (his step-son, who he did not adopt). However my husband died 6 years ago but the stepfather did not change his will so it is left that his estate should go to my deceased husband. As my husband is deceased does the estate pass to my husbands children, or does it go to distant cousins and nephews of the step fathers?

Many of the rules for this are determined by where the will was in effect. What state was this in?

I am in the UK.

And the step-fathers, deceased mothers and my deceased husbands wills were all in England, UK.

This would be a matter for probate to decide.
What is probate? : Directgov - Government, citizens and rights (http://www.direct.gov.uk/en/Governmentcitizensandrights/Death/Preparation/DG_10029799)

Does the will refer to the step son and heirs or just the step son? That could make a difference. But in either case, an executor is probably needed to take charge of the assets in the estate and transfer them to the heirs. And that's a matter for a probate court.

Just the stepson, no one else is mentioned.