First time mortgage- uk and usa couple

Ok hive mind.  I have been here 30 years but didn’t do my mortgages/ tax correctly over the years so only unwound it when we paid it off etc

Usa dual national Daughter is going to buy with a uk husband
I know that I was recommended to hold less than 10% of the house to minimise capital gains upon sale.
I also know she needs to declare currency implications yearly on her taxes when paying the principle.

Is this still correct and anything else?

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