Arjuna's chariot had 4 horses, or we can say all the important warriors had chariots with four horses.
I want to know how these four horses were arranged, were they placed parallel to each other or were they placed in two rows of two.
As Arjuna's chariot was special, it might have a different arrangement than others.
It would be better to give reference to verses, instead of referring to pictures.
The meaning of pārṣṇi and its related words – frequently used in the battle scenes of Bhīṣma, Droṇa and Karṇa parvas – suggests that all major warriors had their chariots drawn by four horses standing parallel to each other. The two outside horses each required a separate charioteer.
pārṣṇi f. the extremity of the fore-axle to which the outside horses of a four-horse chariot are attached (the two inner horses being harnessed to the dhur, or chariot-pole), MBh.
pārṣṇivāh m. an outside horse, MBh.
pārṣṇisārathi m. dual number. the two charioteers who drive the outside horses (cf. prec.), MBh.
E.g., Yudhiṣṭhira, while recounting his battle with Karṇa (from which he had to retreat) says his two pārṣṇi charioteers were killed:
Yudhishthira said, "Welcome, O thou that hast Devaki for thy mother, and welcome to thee, O Dhananjaya! The sight of both of you, O Acyuta and Arjuna, is exceedingly agreeable! I see that without being wounded yourselves, you two, his foes, have slain the mighty car-warrior Karna! He was in battle like unto a snake of virulent poison. He was accomplished in all weapons. The leader of all the Dhartarashtras, he was their armour and protector! While fighting he was always protected by Vrishasena and by Sushena, both of whom are great bowmen! ... In gravity he was unfathomable as the Nether world. The enhancer of the joys of friends, he was like the Destroyer himself unto foes! Having slain Karna (who was even so) in dreadful battle, by good luck it is that you two have come, like a couple of celestials after vanquishing an Asura! Today, O Acyuta and Arjuna, a great battle was fought between myself exerting with might and that hero resembling the Destroyer himself, while seeking to exterminate all creatures! My standard was cut down, and my two Parshni drivers also were slain by him. I was also made steedless and carless by him in the very sight of Yuyudhana...
The Sanskrit verse is:
08,046.011a tena ketuś ca me chinno hatau ca pārṣṇisārathī
08,046.011c hatavāhaḥ kṛtaś cāsmi yuyudhānasya paśyataḥ
There is no reason to suspect Arjuna's chariot were drawn any differently. Kṛṣṇa was most likely steering the two horses in the middle.
