This type of glass pattern is called hobnail and was very common for decanters in a tantalus. There would be 2, 3 or 4 bottles in the tantalus. They would be identical and usually unmarked. The cut would be basically identical no matter which company made them. The stoppers both look suspect to me. The spherical one does not sit in far enough - which you noted, the other is not quite spherical(from the first photo), and it normally was for this type of decanter.
If they are old the glass will have a faint brown tinge, but if it is crystal it will be a faint grey colour. If they weigh different amounts you probably have one of each.
Age? Hard to determine as this type of decanter is still being made and I suspect that even an expert holding them would need to be vague.
Value? It as what the market will pay. Value resides in the eye of the buyer, not the seller.
Ross