Answer: Soilless mix is potting mix formulated for container plants, usually based on milled spagnum peat moss and/or bark plus perlite or vermiculite. It should be somewhat acidic due to the ingredients. I would expect cactus mix to be somewhat alkaline in pH so would not try that. I would discard the shavings or packing material from the package and use fresh soil mix.
You can set them outside in a sheltered spot out of the wind as long as it is above freezing. Freezing will damage the foliage. Protect them only when it is cold, meaning below freezing. You do not want them to get too warm too soon. (House temperatures are too warm unless you have a spot cooler than 45 degrees.) So the shed would probably be better than the house as long as it stays above freezing. Your goal is to keep them below 40 to 45 degrees but not so cold that they freeze.
You do not really want to encourage them to grow yet. You are just trying to keep them alive and as healthy as possible until you can plant them in the ground outside. Once planted, they can wake up naturally with the season. If you had a cool greenhouse it would be much easier than trying to hold them under regular home conditions. Good luck, it won't be easy.
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