My father is deceased. I also cannot fill in this form properly.

You can leave one blank. It worked for me.

so divorce means you no longer have a mom / dad ?

No, it means you see your mother x times a year and your father y times a year...

Fortunately, you can average X and Y, or take the more pessimistic answer and use min(X,Y).

You could also do it twice. Once with both inputs as your dad's age and the average number of times you see your dad and the other for your mom, to get separate estimates for each.

In addition my parents were born in and currently live in different countries.

I do have the same situation since a while (country of living, they didn't change their country of birth ;)). I could understand that not being included, as it is unusual. You cannot cover all with "simple".

The underlying point is that divorce is not unusual, but the norm in some countries.