Obtain Probate estate previously not dealt with

Dealing with an estate surviving spouse has passed away. The property is in the sole name of her late husband who passed away over 20 years ago. It seems that on the passing of the husband his estate was never officially dealt with. No Grant obtained, property left in his name and it doesn’t seem like organisations such as utility companies were ever formally notified of his death. Wife has now died intestate leaving children. In order to deal with the property am I right in thinking that we will need to apply for a Grant in husbands estate first or at the same time as the application for wife? In terms of valuation, for husbands estate we will need to obtain a historic market value of the property as at his date of death?

In terms of completing IHT forms for the husbands estate the difficulty is other than the property it is unclear as to what his other assets and liabilities would have been back then. How do other members deal with historic grant applications when there is very limited information available as to the estate at date of death? Thank you