How to convert multiple objects into SEPARATE symbols?

Yes, distribute them on separate layers as recommended by @kglad ,
then run this script to convert them all into individual symbols:

(function(){
	var doc = fl.getDocumentDOM(),
		tml = doc.getTimeline(),
		cf = tml.currentFrame, i, el;

	doc.selectNone();

	for( i = 0; i < tml.layers.length; i++ ){
		el = tml.layers[i].frames[ cf ].elements[0];
		el.selected = true;
		
		// Here you can change the symbol type or the registration
		doc.convertToSymbol( "graphic", el.guid, "center" );
		doc.selectNone();	
	}
})();