If your dad is remarried after the death of first wife and married less than 10 years, what can be do about property?

Length of marriage makes no difference. One day of marriage means they were "married." The assets would pass under the intestate laws and depending on whether the wife takes exemptions and allowances, she would be entitled to roughly the first $200k of assets and half of the remainder. Of course, this refers only to "probate assets," which are assets titled in your father's name ALONE. Any assets which were jointly held or which named the wife as beneficiary automatically pass to her, and they are not counted as part of the figures above. Most of the time, married couples hold title to their assets jointly. If that was done in your case, the children would not be entitled to anything. I am very sorry for your loss.

it depends on the State laws of intestacy. In Michigan, generally, half of his estate will go to his second wife, the rest divided among his children. See an attorney before the property disappears.