Monica,
If the wood has been allowed to acclimatise to the humidity of your house and the overall size of your post is around 100mm square, then you should be OK.
Clamping up such a job will require a fair few good clamps and cauls (pressure pads of wood not being glued - wax them to stop them sticking accidentally, to spread the load and protect the surface of the glued wood from indentations). I recommend a dry run first.