The sunnah method of carrying a janazah is mentioned as follows:
First carry the left front of the Janazah on the right shoulder (this will be the deceased right shoulder) and walk ten steps. Then carry the left rear on the right shoulder for ten steps. Then carry the right front on the left shoulder for ten steps and finally the right rear on your left shoulder for ten steps. Great merit has been mentioned in the Hadith for carrying the Janazah for at least forty steps.
My question is whilst a person moves in the sequence mentioned above, how do the other three persons move?
The method of carrying the Janaazah in this manner has been mentioned in the books of Fiqh, and has been regarded as virtuous. However, while this is so, the Janaza must be lifted and carried by people. It therefore means, that besides the one who practices upon this, others would have to hold on to the other three ends of the tray/coffin/box to carry the Janaazah.
In normal situations, when the Janaazah is ready to be carried, it is clearly understood that four persons will lift the body to take it to the graveyard. When these four people lift the Janaazah, it is seen that many others come around the Janazah and take turns in lifting it, while it is being carried. The hadith therefore speaks about the meritorious way of carrying the body, which means that this will be practiced by a person or persons while the Janaazah is already on the shoulders of others while being moved. As such, when a person moves in the sequence mentioned in your question, the other three ends/legs of the Janaazah would be carried by others who would have been following the same sequence at different intervals, or they can be of those who are carrying the Janaazah on the other three ends without taking a break.
And Allah knows best.
Mufti Waseem Khan