There are many methods today on how to combine two or more colonies but the one I use that’s quick and have a high success rate is by mixing a 1:1 ratio of sugar and water plus a three to five drops of vanilla extract (mint extract can also be used along with other scent masking liquids) into a spray bottle.
I begin by spraying the colony that has a queen first, including the queen herself, and then spray the bees that I will combine with the queenright colony. Make sure you spray all the bees pretty good to mask their current scent. The bees will then mix and lick each other clean and very little to no fighting will occur. I use this method when it’s warm because the bees will get wet and be sure to ant proof the hive before you do so because the sugar water can attract ants.