Should this be necessary to utilize amcl?

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Hello, I'm using ROS melodic(not ROS2) on Ununtu 18.04.

I'm currently working wrt mobile robot navigation, and I'd like to make some robots move following amcl node with a prepared global map.

However, as far as I've heard, it is imperative to get the mobile robots' initial spawn poses to be matched with the initial poses when I executed gmapping node, to get a global map.

My mobile robots which should be spawned on the Gazebo simulation are 5 indeed, and I think it would be rather hard work to execute gmapping node for every mobile robot because the land is too broad.

If I have to do that 5 times, I think I can't help doing so, but if I happen to don't need to, would you please give some advice?

Thanks in advance. :)