(I have read the entire previous discussion and now simply do not want to quote every single tiny detail) ...
We came across a plot through acquaintances, which is in a very sought-after location in our area (Bavaria). Basically, plots here are a rare find. The plot, with just under 800 sqm, costs 170K. [...] Things do not look particularly rosy in my company at the moment, and short-time work could start at the end of the year. [...] Our family is putting a lot of pressure on us and insists that we absolutely should buy this plot.
... so briefly and succinctly, this is what I would do in your place (in this order of priority):
1. clarify the buildability of the plot, including with a duplex;
2. calculate the possibility with a financing advisor, taking into account both short-time work and a reduced working time after parental leave (i.e., two max. three-quarter part-time jobs);
3. have a firm talk with the family: only those who also open their wallets should have a say;
4. find another young family with whom to build a duplex on the 800 sqm;
5. enter in the forum search that you want to read all posts in which I mention the #goalkeeperthread, so your duplex will succeed.
(6. depending on the slope of the plot, also read the posts about the 11ant basement rule).