Update:

So my dad checked the tyres in. As you can see in the main post, 2 tires are duct taped to each other instead of having all 4 of them separately.
Firstly, they didn't fit in the boot of the Mercedes E200 chauffeur (was the saloon, not the estate) so they had to be in the back seat.

Secondly, at check-in, for some reason the staff didn't allow 2 tires to be taped together so they checked them in as 4 separate pieces.