You would not need to have 25 child tables as you could have an identifier in the log table to identify the field.
But maybe in your case, yes set up 25 log fields and 25 form rules to populate the log fields.
The there is a formula I can help with to count the # of updates. So you will need 25 formuals. Then you will need 25 more formulas to to parse out the most recent date update.
I think if I had to that somewhat ugly project I would use a child table. you can have I think 20 Automations per table to trap 20 date field changes and 10 Actions to trap the remaining 5.
Otherwise you need to use a webhook to log all 25 when any of them changes and then using an automation delete out the date changes that did not change.
This is just an overview - due to the large # of fields to be tracked its not a trivial project.
