We're trying to make hard crack candy,the humidity in the house is 50%
50% RH does not sound so bad actually.

In a hot-humid climate, chilling the food will only exacerbate the problem of condensation.

There are a few options. Put them into an air tight container with some food grade silica gel desiccant. Alternatively, a bowl of salt (you can pre-heat the salt slightly) will do a similar job. 

Use a food dehydrator, but you will still have a wetting/sticky problem during storage.