They are very pretty! I don't know what they might be mixed with. Their size might give you a clue, but it could be so many things, including another mix.
It's a little hard to tell on the profile picture; she almost looks chocolate there. So maybe a blue with rust? She looks a little dark to be lavender to me.
I'm not entirely sure what the genotype of fawn and white runners is, but I think it has at least 1 blue gene and chocolate. If so, you'd probably end up with blue pied and lavender pied ducklings. If fawn/whites have only 1 blue gene instead of 2 (someone else might know), you could get black...
This is what you can get from all colors with either a blue drake or a blue drake split to chocolate.
With the chocolate gene in either a hen or the drake or both, you have lot of possible duckling colors!
This is one of my lavender hens vs my lilac. Lilac almost looks buff, with a caramel tone.