FWIW, Timo has also mentioned using a Koch Powertone, a 5150, and a Revv Generator on various recordings, and his artist presets in the Double Impact Ultimate Bundle 2 use profiles of a Framus Dragon and an Orange Rockerverb. His live sound with Delain seems to be pretty consistently the Dual Rec, though.
Merel is probably using a profile of her Engl (a Ritchie Blackmore, AFAICT), but she's also shown photos of having a Dual Rec, a 5150, and a Revv Generator in the studio for reamping in a Purest of Pain session. (At least the Revv appears to be borrowed from Timo.)
You are definitely right about the Engl. In the video at the top of the thread she says that its a Ritchie Blackmore. Thanks for the info about Timo. I'll have to checkout the double impact bundle.