So glad you came here, Charles.
Yes, some brugs smell different than others, but they all are quite fragrant at night. Their pollinator is a night-flying moth, I think. So they attract the pollinator to them by releasing the scent at night.
Now, the question about whether they will come true from seeds sort of depends upon IF you actually have the right moth where you live. If your different kinds of brugs cross-pollinate (which surely will happen if you have the right moths) then you'll get crosses of your brugs. i.e. they won't come true. Now that's not always a bad thing, you might get some really neat flowers.
But if you want to make sure to get one that is true to the parent from seed, you need to isolate it somehow (if you have a screened porch that would work) and pollinate it yourself with a little paint brush or maybe a Q-tip? I don't know what to use as I've never done it myself, but @gone2seed
will know what to use.
We do have the moths here although I've never seen them at the brug flowers, but mine just happily cross, and I have some seedlings coming along that I have no clue what they might be.
Easier, and a sure way to get the same plant, (I think) is just to take cuttings and start them the same way you did with the yellow one. I put them in water until they start to make roots, which usually only takes about a week. Then just pot them up and stand back! (well, except for when you're watering and fertilizing them . . . )