Genealogy is like house dusting. When you think you’ve got it done, it seems like there is more or something that you missed. Or a new spot of dust appears and it’s just begging to be wiped away (or researched to stretch the metaphor).
If completing the 5-generation genealogy book of your ancestor’s descendants is too much, start smaller. Work on just the grandchildren of the couple and try and document those individuals. If that project seems too large, work on writing up the ancestral couple as much as you can. Write up what you have. Cite your documents or sources as you go. Try and research the couple as much as you can, but writing (even if just for yourself) can cause you to notice gaps or omissions in your research. And that’s a good thing. Admitting you aren’t done is ok–in fact it’s more upfront with your readers to let them know that you know there could be more out there.
But at least you wrote and preserved something.