I suspect both these are Heuglin's Gulls. The first a near-adult, the second and 2nd or 3rd winter, though difficult to say for the latter.
Adult Yellow-legged Gulls have pale grey upperparts, very little streaking at this time of year and a large white mirror in the outer primaries.
An immature would, in comparison with the bird photographed here, be largely white on the underparts with a brighter yellow bill base.
Geoff