Edison joins Apposite from Jefferies International, the US-based investment bank, where she was a healthcare investment analyst.
Montagu has exited Nemera, which makes devices including inhalers, insulin pens and pumps, after a four-year hold.
The Elix exit will provide Sun with a timely lift after it had to let go of golf retailer American Golf, which was sold to Endless in pre-pack administration.
American Golf, previously owned by Sun European Partners, has been looking for a buyer in a tough retail trading environment.
Tikehau Capital and Bpifrance will jointly own around 24 per cent of GreenYellow with the remainder held by French retailer Casino Group.
Equistone acquired a majority stake in Dutch business Group of Butchers in early 2017 from Nordian Capital Partners.