Fschifano is correct, AFAIK. I'll add that Arista II is reported to be Agfa. Note this means that both the Arista Pro and Arista II lines are going away and are probably in short supply.
Another point: Freestyle uses the same names for its papers, with mostly the same manufacturers, but I believe there may be one or two exceptions. The Arista.EDU Ultra paper is Foma and I think the Arista.EDU paper is Forte, but the Arista II paper is supposedly rebadged Kentmere (Freestyle claims it's made in England). Freestyle still has some limited stock of Agfa paper under the "Freestyle Private Reserve" name.
As to the original query about how these films compare to TMX and TMY, these Kodak products are both T-grain emulsions, but most of the Arista line are conventional-grain emulsions. The old Arista Pro D-Max films were rebadged Ilford Delta product, but I don't know if Freestyle has any of that stock left. I've seen conflicting claims about whether or not Fomapan 200 (aka Arista.EDU Ultra 200) is a T-grain film, but the 100 and 400 versions of these films definitely are not T-grain emulsions. The Fomapan/Arista.EDU Ultra films (especially in the 100 and 400 speeds) have unusually crisp grain structure, even in developers that normally produce mushy grain. The grain isn't particularly fine, though, unlike the T-Max films, and as conventional films, the grain structure has a more conventional look to it. Kodak's T-grain films have different spectral sensitivity than most B&W films, which means they do a better job with sky than do most films. If anything, I'd say the Foma/Arista.EDU Ultra films are worse than average in this respect, but they might just be average. I'm less familiar with the other Arista products (aside from Arista Pro 50, which is Ilford Pan F+ and is in short supply, if they've got any more of it at all), so I can't comment on them.
As to how often Freestyle changes suppliers, I don't know that, offhand, although the recent changes have been as a result of general upheavals in the photographic industry. I can say that, although Freestyle uses the "Arista" name in all of their films from different suppliers, they've given each supplier's line a different sub-name, as fschifano details. If you know this and pay attention to the sub-name, you won't shoot a roll and develop it only to find that it's something other than what you expected, at least not unless Freestyle changes its practice on this matter in the future.