British and European champion Steadman, 20, and 36-year-old former world champion Cunningham are both former Paralympic swimmers.
Steadman switched sports following her appearance in the pool at London 2012, while Cunningham won gold at Barcelona 1992 and spent a decade away from elite sport before taking up paratri in 2008.
McClelland, who has won each world title in her category since 2010, missed most of 2013’s major races while she wrote her university dissertation – but still proved too strong for her team-mates at Hyde Park.
The Tri 4 category, in which the three compete, includes athletes with arm impairments.
Derby’s Ellis, alongside guide Luke Watson, won the Tri 6b visual impairment classification, with Cornwall’s Reid adding the women’s equivalent to her European gold.
Emmerson successfully defended his world title in the men’s Tri 5 leg impairment category.
