The PCN is badly printed with many data fields seriously displaced, but whether that's enough to make it void, you'd only find out at London Tribunals. Time of alleged contravention is 16.19, so well inside the restricted time, that you say ends at 18.30.
as family member thought weekend were fully free for single yellow
Oh dear ! Never,
ever, assume anything about parking in London, always look for the sign if you're parking on a single yellow line.
Frankly, I see nothing to refute the contravention itself, but that doesn't mean 'game over' as there may be a 'technical' appeal argument based on the council management of the enforcement process incl the content of the PCN. This would include bad printing of it, rendering it void.
So wait a bit to see what the others say, but don't miss any deadlines on the PCN.