I haven't (successfully) tracked shared assets like this, only shared expenses. I think I'd need a stronger separation of those accounts to avoid confusion. Eg if I really wanted both my and household transactions in one journal, I might do the following
(I've just used equity for household as @shlewislee suggested):
# me+household.journal
2024-01-01 my contribution
me:assets:bank -100.00 EUR
me:expenses:household 100.00 EUR
household:equity:me -100.00 EUR
household:assets:bank 100.00 EUR
2024-01-01 my partner contribution
household:equity:partner -100.00 EUR
household:assets:bank 100.00 EUR
2024-01-02 pay shared bill
household:assets:bank -100.00 EUR
household:equity:me 50.00 EUR
household:equity:partner 50.00 EUR
Or, I'd go the extra step and split the files:
# me.journal
2024-01-01 my contribution
assets:bank -100.00 EUR
expenses:household 100.00 EUR
# household.journal
2024-01-01 me contribution
equity:me -100.00 EUR
assets:bank 100.00 EUR
2024-01-01 partner contribution
equity:partner -100.00 EUR
assets:bank 100.00 EUR
2024-01-02 pay shared bill
assets:bank -100.00 EUR
equity:me 50.00 EUR
equity:partner 50.00 EUR
Or, if I needed more detailed reports from household's point of view, I could record expense categories:
# household.journal
2024-01-01 me contribution
equity:me -100.00 EUR
assets:bank 100.00 EUR
2024-01-01 partner contribution
equity:partner -100.00 EUR
assets:bank 100.00 EUR
2024-01-02 pay shared bill
assets:bank -100.00 EUR
expenses:foo 100.00 EUR
#2024-01-31 retain earnings (splitting them 50-50)
# expenses ==* 0 EUR
# equity:me 50 EUR
# equity:partner 50 EUR
I haven't done it, but I think all of those could be generated with (multiple runs of) CSV rules (except retaining earnings).