An update...
The issue was trying to load several mbtiles while having respective popup interactions for each layer (each mbtile included interaction, created in TileMill).
I opted to load the mbtiles to the map using:
var base1 = L.tileLayer("http://ms1.mysite.com/folder1/mbtiles-server.php?db=base1layer.mbtiles&z={z}&x={x}&y={y}.png"
var base2 = L.tileLayer("http://ms2.mysite.com/folder2/mbtiles-server.php?db=base2layer.mbtiles&z={z}&x={x}&y={y}.png"
Then added interaction from a separate geojson file.
var onEachFeature_Polygon = function (feature, layer) {
//polygon geojson file contains center points
var centerLat = feature.properties.y;
var centerLon = feature.properties.x;
var centLatLon = new L.LatLng(centerLat, centerLon); //this is used to place the popup in the "mouseover" function
layer.setStyle(tooltip_default_style);
if (feature.properties && feature.properties.Name) {//fields Name, Population, RI10K
var list = "<b>" + feature.properties.Name + "</b>" + "<br>" + "<i>" + "Population: " + feature.properties.Population + "</i>" + "<br>" + "<i>" + "Income 10,000+: " + feature.properties.RI10K + "</i>" + "<br>";//end of tooltip list
layer.bindPopup(list);
}
layer.on("mouseover", function (e) {
layer.setStyle(tooltip_hover_style);
layer.openPopup(centLatLon);
});
layer.on("mouseout", function (e) { layer.setStyle(tooltip_default_style) });
}
//this is the onEachFeature function called when the statsJSON layer is added to the map
var statsinteractive = new L.GeoJSON(statsgeo, { onEachFeature: onEachFeature_Polygon });
statsinteractive.addTo(map);
Would still like to understand or be directed to a clearly outlined method to 'call' interaction from an mbtile file.
In the meantime, I hope this is helpful for someone with a similar issue.