This will be easy for you to do in software, given your database, but very hard to do manually.
I want to be able to select any LIVING person in the tree, and have you display (with the percentage of shared genes) all and only those living persons with at least 1% of their genes shared with the highlighted person (and the tree to their common ancestor(s). (1% could be a parameter, but I think there is little interest in anything smaller.)
The algorithm is not complicated, but it cannot be easily done manually (too compute intensive). You might even want to patent your finished algorithm (or at least publish it.)
Essentially, given that A is highlighted for calculation, reject if not flagged as living. Next you look at each person in the tree that is both living and has a common ancestor (male or female) with person A. Eliminate those where there is no common ancestor recorded or are dead.
Now it is relatively easy to calculate the percentage of genes shared for each remaining person with person A, and then to provide a tree display showing only the persons that share at least 1% with person A, together with the complete tree back to the common ancestors.
Of course there are complications arising from adoptions, multiple marriages, identical twins etc etc. The algorithm can never be perfect, and the tree data is not perfect anyway.
John L