Certified GKH Gardening Expert
The seeds of Tweedia should be fairly easy to germinate; they do need bottom heat though.
Heat the bottom of the nursery tray with a warming mat set to 70 degrees Fahrenheit if you are germinating the seeds indoors where temperatures are typically cooler. Leave it at 70 F at all times during the germination process.
I hope this helps your germination of this particular variety. Also verify the quality of the seed you have. If you are successfully germinating other types; perhaps it's worth talking with the company you purchased the seed from.