The core rulebook states that if 2 things would happen at the same time, the player whose turn it is gets to decide which order they occur in.
I'm away from my DftS at the moment but believe that as soon as those flyers finish their movement the attack patterns kick in.
I dedicate these deaths to Odin Allfather, Spearshaker, One Eye.
Fleet Shadowmaker - Kabal of the Dying Sun; Cult of Marrow Excised; Coven of Lambent Hunger
Sons of the Last Breath - Chaos Space Marines
Host of Shattered Purity - Chaos Daemons