Load BYG's Biomes(All dimensions). Steps: 1. Create a new world and import these settings. 2. Enter the nether/end and double check that it worked. Server Owners Only: 3. Exit the world and make the world your server's world. 4. Ensure that level-type=byg is in your server.properties. 5. Load the server. 6. Enjoy.

BYGDimensionSettings.json

{
  "dimensions": {
   "minecraft:overworld": {
      "generator": {
        "biome_source": {
          "seed": -1464245863,
          "type": "byg:bygworld"
        },
        "seed": -1464245863,
        "settings": "minecraft:overworld",
        "type": "minecraft:noise"
      },
      "type": "minecraft:overworld"
    },
    "minecraft:the_nether": {
      "generator": {
        "biome_source": {
          "seed": -1660337403543655964,
          "type": "byg:bygnether"
        },
        "seed": -1660337403543655964,
        "settings": "minecraft:nether",
        "type": "minecraft:noise"
      },
      "type": "minecraft:the_nether"
    },
    "minecraft:the_end": {
      "generator": {
        "biome_source": {
          "seed": -1660337403543655964,
          "type": "byg:bygend"
        },
        "seed": -1660337403543655964,
        "settings": "minecraft:end",
        "type": "minecraft:noise"
      },
      "type": "minecraft:the_end"
    }
  },
  "seed": -1660337403543655964,
  "generate_features": true
}