Both attackers are yet to be capped by the Selecao.
Rayan, 19, joined Bournemouth in January for £24.7m from Vasco de Gama and has quickly settled on the south coast, scoring twice in the Premier League.
"Really proud of what he's done to get to this point. He's been here for nearly two years and I've seen that journey closely and I know about his overall journey to get to Europe and the Premier League," said Brentford manager Keith Andrews, after Monday's 2-2 draw with Wolves, in which Thiago scored.
"Everybody has played a little part in this. We should all be very proud of Thiago's dream coming true.
"It has been a dream and a huge ambition for him. When he pulls on that iconic jersey it will be a special moment for Thiago and his family and we will feel a sense of pride."
Former Norwich City midfielder Gabriel Sara is also named in the Brazil squad for the first time.