According to French outlet Foot Mercato, PSG sporting advisor Luis Campos has opened informal talks with West Ham's leadership regarding both players.
West Ham are believed to be seeking around €50m for Summerville and €80m for Fernandes, a combined total of roughly €130m.
The interest comes at a difficult time for West Ham United, who were relegated from the Premier League at the end of last season after finishing 18th with 39 points.
Summerville, 24, was one of the few bright spots in a difficult campaign, contributing five goals and four assists in 31 Premier League appearances.
The Netherlands international joined West Ham from Leeds United and previously came through the youth ranks at Feyenoord and ADO Den Haag.
He is currently away on international duty with the Netherlands at the World Cup, meaning any final decision on his future is expected to wait until after the tournament.
Fernandes, 21, made his Premier League debut with Southampton before joining West Ham, where he scored three goals and added four assists in 36 appearances this season.
The Portugal international is a product of the Sporting CP academy and is also being tracked by Manchester United and Real Madrid.
For PSG, pursuing Fernandes would continue a recruitment pattern under Campos of targeting Portuguese players, following the earlier additions of Vitinha and Joao Neves.
Adding Summerville, meanwhile, would address a stated need for PSG to strengthen out wide following the back-to-back European champions' push to deepen their squad.
No formal offer has yet been submitted for either player, with talks described as preliminary at this stage.
West Ham face significant financial pressure following relegation and are widely expected to need to sell several first-team players this summer to balance the books.
Selling both Summerville and Fernandes for fees close to West Ham's stated valuations would represent a significant boost to the club's transfer budget as they target an immediate return to the Premier League.
Whether either deal progresses may depend heavily on competition from other interested clubs, with West Ham under no obligation to accept the first offers that come in.
For PSG, completing both signings would represent a substantial outlay, but one that fits a squad-building strategy aimed at maintaining their dominance domestically while pushing for further European success.