This all goes toward the screening rule. Bear with me, this explanation is going to be long.
Anytime players are standing close together, the potential for a screen exists. Close together is normally defined as an arm's length or less apart. The word "potential" is used because the ball must be served over these players in a low trajectory for the screen to be called. Additionally, a single player standing near the server could create a screen if he is upright and the server sends a low trajectory serve directly over that player. Another single player screen can be created if they are deliberately moving to block the view of a receiving team's player. It's important to note that the receiving team players are not guaranteed any specific spot on the court to receive a serve. Therefore, they must move if a single player from the serving team is blocking their view of the server. However, if they move and the same serving team player follows them to continue to block the view of the server, a potential screen exists. Again, the ball must be served over that player.
For your team's serving formation, the only way a screen would be called is if the two upright players had their arms fully extended and a low trajectory serve went over the group of players. If their arms remain at shoulder height or lower, no screen potential exists. The second situation is exactly what was described above, and a screen potential exists. It's important to note that just standing together is not illegal. The ball must be served over the group in a low trajectory.
Generally, the officials will use preventative officiating and warn teams of a potential screen.