A tweet on Legendary's official Twitter page has confirmed that Mothra, Rodan, and King Ghidorah will be featured in the sequels.
It is not confirmed if they will be in one or both sequels that have been previously announced.
Also another tweet confirmed (and was also announced at SDCC below) that Gareth Edwards will direct the next installment as well.
"We get to make another one! But first I need a break from the pressure of working on a major franchise, so I'm here in San Francisco doing a little scifi film (a Star Wars one)." Yes, Edwards will be back to direct Godzilla 2, he confirmed.
Next came a bit of teaser footage showing warfare and "A secret remains hidden. There are OTHERS." A flying monster - yup, it's MOTHRA confrimed for the sequel. GHIDORAH confirmed for the sequel. "Conflict inevitable... Let. Them. Fight."
"Now we have more monsters to play with and we're excited about," Tull said, "Thank you Comic-Con, it all started here and we can't wait to show you more."