I already guess that it is obvious that the horse you said was the one ridden by the MC itself, but sadly not sure about the rest.
Satono Diamond looks different though. He only has a small diamond-shaped "star" on his forehead.
Hmm... when the 2018 cross-promotion campaign was going on, there was also an exhibition featuring a 1/48 scale (~15 inches tall) Gundam RX-78-2 in Kitasan Black's colors. To commemorate Kitasan's victory during the previous Arima (in 2017).
The horse being ridden by the RX-78-2 here does look more like Kitasan. Coat a little too light-colored (could be the lighting), and stripe a bit too thin, and too pointed near the forehead. Though... hmm... if one considers, say, a hypothetical lovechild between Satono Diamond and Kitasan Black (average both their coat colors and merge Dia's diamond to Kitasan's stripe)... the result will look eerily similar to the above. Hmm.
Interestingly, they ran another cross-promotional campaign in 2019, this time featuring Gundam Seed and the 2019 Tenno Sho (Autumn)... with Kira's Strike Freedom painted in Kitasan Black's colors. There was even a 1/144 scale model available for sale (unlike the previous exhibition-only Gundam), though I think it is a rare collector's item.
