I use to put a mesh between two colonies that they get same odor.
This is very good tool to give the queen.
Before joining put the queen under the cage.
If bees do not bite the cage, they accept it. Let it be there to next day.
If colonies are equal size, you just put them together. 1:3 is enough too.
Yoiu may pour surup on combs that small colony such syrup stomach f