I wouldn't give Hannah a main draw WC. It automatically uses up 1 of her WCs as she gets a ranking point just for playing. Leave it as a qualifying WC and as there's no ranking points for a 1st round qualifying loss it doesn't count against her WC limit if she loses, and if she wins she gets a few more points for that WC.
My guess would be Marni. It should be someone that doesn't need to play the WC play-offs later in the week.
Be strange not seeing Heather at Birmingham this year but on the other hand she may get more points in Ilkley so might be a smart move. I assume she will be at Eastbourne.