I’m not sire I fully understand, but I will offer a couple of thoughts while you wait for some better replies ….
If you have a DNA match in the Urch tree it might not mean that you and your son in law are “related”. Could it be that you are related to someone else in the tree who married into the Urch family?
There are often errors in trees attached to DNA results, so keep that in mind. Many of them only show direct lines and to find where you match you often have to search very wide …. For example trace all siblings of all 4 and 5x great grandparents, and then trace their descendants on all lines ….
I would look at mutual matches of you and the Urch match to see if that clarifies.
Lastly 8cm is a small amount of DNA to share. I think it is Ancestry who have a cut off, and don’t even bother to show matches that low. Having said that, some people are able to trace matches which share very low amounts.
It is a good idea to test your son in law too. DNA is passed down randomly and it could be that he did not inherit DNA from the same ancestors that you did.
There is loads online but this American one explains the possible time lines quite simply
https://www.familyhistoryfanatics.com/how-far-back-ethicityRegarding paying someone to research for you, I would think they would just do the same sort of online research tracing all lines, in the same way that you would. Others may have some suggestions on this.
Good luck, and pop back when you get your son in law’s results.
Added: which company did you take the DNA test with?