I appreciate the help I'm receiving here, even though I have semi-manually achieved the split.
I have followed your instructions to the letter. Generations are 99 up and down. Generation of the Extended chart took very little time, deletion slightly longer. Far, far longer was the regeneration of the chart with me (home person) as the base - an annoying step which I wasn't able to prevent happening, or to interrupt.
I'm wondering if scale has something to do with my problems. Before splitting my tree, it contained some 19'300 persons. Now that I have removed my wife's part, I'm down to 17'200. After painful completion of the multiple deletions, I was able to manually remove several hundred unwanted places (out of about 3'500) and then compacted the remaining file, achieving a compaction of some 30%.
Now comes the astonishing part. The original file has a size of 48'295 kB, but the reduced file (containing 2'000 fewer persons and 400 fewer places) has a size of 49'433 kB. Both are compacted. I don't have many media files, but anyway this should be irrelevant. How can a reduction INCREASE the file size?