Is it possible to use the gallery in one page(modular)? I am using photographer theme.
You would need to adapt the regular template page into a modular page. The complexity of this depends on the current theme.
I’m assuming there’s a header with information about the photos, and a twig template that renders that. If that’s the case, then really you just rename the page and prefix with an underscore to tell Grav it’s modular. Then you take the template and copy/move it under the templates/modular/ folder in your theme, so Grav can find the modular template for the gallery. Then you just use it as a regular modular page.
I mean two gallery in one modular page. Can i do that?
You can do anything 
It might just take some modification and tweaking.