OK, here's my guess on your photos. I'm sure others will join in the guessing game. Some are a bit difficult without flowers, or indeed, knowing the pot size for the plants shown. But it makes it a bit harder that's all
#1 looks like M. longimamma or maybe sphaerica
#2 has bristles in the axils, and though the spination isn't "typical" looks like a form of M. mystax to me.
#3 is a form of M. formosa. The description in Pilbeam is very specific on M. formosa - 6 central spines, but this species varies very considerably and this looks to me like a form of which I have a couple of plants. Check Rog 326 towards the bottom of the Formosa section in the A-Z gallery
#4 I am unsure about, though it could be M. backebergiana
#5 looks like M. rhodantha
#6 could be the white flowered form of M. zeilmanniana. I don't think it is M. mathildae, which is another white flowered member of the Stylothelae. Did you notice what the filament colour was when the flowers were open? M. mathildae has pinkish filaments.
#7 another probably poor guess on this one - M. pettersonii? possible what used to be called apozolensis saltensis?