This is lamp work - i.e. fashioned from glass tubes in a gas flame, so not actually done in a glass works in front of the oven. Chances are your swans were made in China or in Lauscha (Germany) - but remember lamp work can be done anywhere and does not require great investment.
Riedel invented the colour, but his production (19th ct.) was very bohemian, quite heavy, panel cut, gilded, ornamented and decorated - so no relation to your swans.