Mother and father level of education into a single index/variable

#1
Hi All,

I hope this post finds you all well! :)
I am conducting a research on the educational attainment of children of immigrants. Two of my control variables are the level of education of father and the mother of the child. I have been suggested to combine these two variables into one, but I cannot find any article in which similar variables are merged together.
Both of my variables are categorical and are structured as follows:

What's your mother/father highest level of education?
1.None
2.Elementary school
3.Middle school
4.High school
5.Univesity
6.Don't know

I was thinking to combine the data in a similar fashion: both parents university degree / one parent university degree, one parent high school / one parent university degree, one parent middle school / one parent university degree, one parent elementary school / one parent university degree, one parent none / both parents high school / one parent high school, one parent middle school / both parents middle school / etc.
I can't think of a better way, has anyone went through a similar issue or can anyone suggest an article in which something similar has been done? Any suggestion would be helpful!

All the best,
Marla