Daenerys's color is an odd one; if you're going for an arda, either 063 Silver or AR017 Titanium Blonde will be your best bet. The name "Silver" is a little confusing; it's actually very close to a pure white, but has some very light grey mixed in to give it a more natural look. Titanium Blonde is just a bit too yellow IMO, but it could work as a substitute in a pinch. As far as non-Ardas go, the exact match does exist from some US sellers, but the caveat is that the wigs are non-heat resistant; it's a tradeoff.
For the second wig, a Merry in 064 would be the easiest route, albeit a bit inaccurate in color (both Morgana and Gwen seem to have some brown to their hair).
If you want a bit of a better suited color and you have some time before the cosplays need to get done, there are some options. If the cosplays don't need to be finished for a WHILE, there's the option of suggesting the Merry in 080 on Arda's suggestions list, which is an extremely dark, near-black brown and almost a dead match for both characters. For less time and a bit more work, you could also wait for Arda's next restock for the Le Tigre in 080, and set curls in it (the first two parts of this tutorial
describe the process well, including the important cooling step, you'd just need to piece your curls out a bit more after unrolling them).