Pour a little bit of vodka from each bottle into a separate jar. This will free up space to add the vanilla beans so that it doesn't overflow.
Slice each vanilla bean in half
Place 20 beans in each bottle. Optional, leave a few beans out to add to your separate jar of vodka. Seal the bottles and shake well. Shake daily for 4 months for optimal flavor.
Notes
I used to use twice the amount of beans for this amount of vodka. If prices go down then, add up to 40 beans per bottle. Your extract will be stronger and be ready faster.