Every entity's books are right, and the number you take to the board is still typed into a spreadsheet
The entities are not the problem. Each one closes, each one balances, each one would survive its own audit. The problem is the last mile: three trial balances get exported, someone lines them up in a workbook, someone adjusts what the entities did with each other, and the figure that leaves the building is the figure in the workbook rather than the figure in the system. Which is fine until a question comes back a week later and there are two versions of it, the one in the pack, and the one the ledger has moved on to since.
What changes with finance and reporting
Each entity keeps its own chart of accounts, tax rules and localisation, and all of them sit in one database, so the figures come out of one system in one shape, instead of three exports that then have to agree with each other.
An entity that trades in another currency is held in that currency by the ledger, with the rate, the revaluation and the gain-or-loss account part of the entry rather than a column somebody maintains.
A posted entry is sequenced and hash-chained and a closed period is lock-dated, so the month you already reported can be shown to be the month you reported.