First off, you need to ascertain whether there is a will or not. What is this thing they step-dad originally thought was a will, and what happened to it?
If there is no will, Iowa's intestacy laws govern the distribution of your mom's estate. I assume that 633.212 is the applicable provision here (surviving spouse, and you and your siblings are not children of that spouse). What he gets is:
- 1/2 of all real property (land)
- all personal property (stuff and money) your mom held as "head of the household, exempt from execution" (this is kind of wierd - I suspect it refers to some minimal personal property exemption)
- 1/2 of all other personal property
- if all that amounts to less than $50,000, he gets whatever else is in the estate up to $50,000. If the whole estate is worth less than $50,000, he gets the whole thing.
Basically, he gets 1/2 of everything, unless everything is less than $50,000, in which case he gets it all. Plus he gets whatever personal property she held as "head of household" - I suspect that will be pretty minimal.
If you think the estate is worth more than $50,000, see an estates lawyer.