Sam is a tax adviser on Just Answer who worked for some years for HMRC and the Inland Revenue rising to the grade of Higher Tax Officer, I understand.
The surcharge can be repaid if you sell one of the first properties within 18 months.
If you both own a property and are not married then the 3% surcharge will apply if either buys another.
For CGT purposes, as they are your sole or main domestic residences, Private Residence Relief (PRR) applies which relieves CGT at 100%. If you are married you only have one PRR between the pair of you.
JHave I covered all your points?
Yes as you are not married. At present in tax law your are entirely different persons. Not quite the same were you married.
As far as I can see no as you are merely replacing sole or main domestic residences.
No the taxes are entirely different and managed by quite separate offices.