At the future Buddha's feet is his horse Kanthaka & one of the two other figures should be his charioteer Channa, who later became his disciple. Channa was the one who explained the 'four sights' (old age, illness, death & an ascetic) to the Prince, which inspired him to become a monk.
...with the Panjavakkiya, or his first five disciples - Kondanna (โกณฑัญญะ Konthanya in Thai), Bhadiya (ภัททิยะ Phathiya), Vappa (วัปปะ Wappa), Mahanama (มหานาม) & Assaji (อัสสช Atsachi):
This event is now marked as Asanha Puja, the full moon day of the eighth lunar month, which is also the day before Khao Phansa (start of Buddhist Lent or rains retreat).
On the lower left panel of the gable - Buddha taking his first seven steps after his birth in Lumbini, with a lotus spontaneously blooming beneath his every step, & his mother, Queen Mahamaya, holding onto a branch of a cannonball tree (Couroupita guianensis aka. ต้นสาละ sala tree) at right: