I don't think the first is M. grusonii, but I would suggest it is closer to M. petterssonii in its hamiltonhoytea form perhaps, or perhaps gigantea. The upwards curving, slightly shorter central spine is quite reminiscent of M. wagneriana.
This whole complex - gigantea, petterssonii, wagerniana, obscura - show similarities as well as some differences.
My final guess for a name - wagneriana. But others probably know better......
I don't know the red flowered form of M. brandegeei, but see it was described in the Looseleaf data shets of the AfM. If anyone has these, could they advise Marco?