How to render Multi-Response GeoJSON tiles

The so-called "multiresponse GeoJSON object" is not valid GeoJSON. Split the data before instantiating the Leaflet GeoJSON layers, e.g.:

// Assuming that you've already fetched the data off the network
var data = {
  roads: {
    type: "FeatureCollection",
    features: .....
  },
  pois: {
    type: "FeatureCollection",
    features: .....
  },
  .......
};

for (var featureLayer in data) {
    console.log(featureLayer); // e.g. "roads", "pois", etc
    var geoJson = data[featureLayer]; // This is now a valid geojson object

    // Now we can spawn Leaflet layers based on valid GeoJSON
    var layer = L.geoJson(geoJson, {...}).addTo(map);
}

I am now using Tangram to display my tiles, Tangram allows me to parse the composite response with no issues at all, it can identify the layers with just the name I supply, and it has good documentation and support.