Not sure what the dimensions of the slabs are, or how you want to turn these.
Pine is not a wood I consider good for turning. Potential for resin or pitch.
Search on this forum for "green wood" and you should find a number of threads, perhaps many.
Some folks seal green wood until they are ready to turn the piece, then rough turn, allow the piece to dry and change shape, then turn again to final shape.
Some folks will attempt to replace the water in the wood with PEG (Polyethylene Glycol). Not cheap, but it can replace the water with the PEG molecules and then be "stable" and not crack as it dries out.
I think your choices are to seal and wait until you are ready to turn, then do the two step process, or turn immediately and then allow to dry, change shape, then final turn when dry.
It is not easy to turn immediately, since it takes too long. Better to harvest, seal then plan how you want to turn.
Sealing can be latex paint, paraffin wax, or Anchorseal.