Spawners?

I found 4 spider spawners all right next to each other in survival and was working on making a farm, it’s quite nice.

My question is does having more than one active at a time actually increase spawn speed or will the same amount of spiders spawn just distributed across all four?

Cause I don’t want to kill efficiency of my farm and I could split spawners in 4 different farms if that would spawn more mobs, just need that loot.

Server lag issues?

On my Minecraft server every 5 minutes and 3 seconds I get the error on the server chat that the server can’t keep up, is the system overloaded apparently?

Error like running behind X ticks and so on and ONLY when I (the server host) is online on the server. My friends played for four hours without an once of trouble or lag and when I log on it all the sudden will freeze every five minutes. Any help would be GREATLY appreciated.