Hm. They're intelligent like reploids (to a degree), but certainly not replica androids...
Were Robot Masters Mechaniloids?
Reploids are not replica androids either.
As for question No. 2, refer to Zero's dialogue vs Roll in TatsuCap. Zero calls Roll a housekeeping Reploid.
As far as Robots of the 20XX era go, they are easily mistaken for Reploids, since they have a similar level of intelligence and make-up, although it may not be quite on the same level.
And Online states that Bass himself easily closely matches the level of advanced AI and independence of prototype Reploids. (X, Zero, Sigma)
A Mechaniloid is usually a robot with very limited AI, usually not of intelligent advanced thought capability. Things like Mets. Sometimes they may not even have full independent thought. I would refer to the Mechaniloid from Day of Sigma, which while it seems to exhibit some kind of AI, is still a machine that seems to require a pilot, or in that case, a remote operator.
Pantheons however, seem to straddle the fine line between Reploid and Mechaniloid. They are described as "mentally degraded" Reploid copies of X, so they are considered Reploids, but their intelligence level definitely seems below average Reploids.
Variants and Galleons I have no idea though, they may be Reploids like Pantheons. I dont recall if the databases from Z4 and ZX state anything to that matter.