Legal Question in Wills and Trusts in Pennsylvania

You say both parents died at the same time. Usually that does not happen and its possible to determine death order unless they both died in a plane crash or something like that.

You do not indicate where the parents lived at the time of their deaths or when the deaths occurred or if estates for each are pending. This matters because state law varies.

Most states have what are called simultaneous death acts or something similar. Basically, if the spouses die at the same time such that the death order cannot be ascertained, then each will be considered to have died before the other. The mother's property will pass to the mother's children in equal shares and the father's property will pass to his children in equal shares. Any jointly owned property, like land, will pass 1/2 to father's children and 1/2 to mother's children.

Step children do not inherit from the step-parent. The child only inherits from biological or adopted children.

And how do you know what the mother wanted? If the mother had wishes, she would have made a will. This was especially important as their were step-children involved and neither parent here acted very responsibly by having wills/estate plans made. Since they did not do that, any wishes the parent may have expressed verbally are irrelevant. There is no will so all of the mother's possessions must be split by the mother's children only and the father's possessions are split by the father's children only.

Once things have been distributed or tenatively distributed after the bills/debts of each estate have been paid, if the children want to make their own family settlement agreement that is up to them.

I would suggest that mother's children seek out a probate lawyer and father's children seek out a probate lawyer here because of the possibility of a conflict of interest.