Hi Davinder,
SAML 2.0 supports Multi-domain Web Single Sign-On, therefore even though you will have users accessing resources through different domains, this can be achieved with SAML 2.0.
In the Mobile layer, SAML 2.0 alongside an OTP (Mobile Authenticator) solution will probably be the best approach.
Please refer to the OASIS SAML 2.0 Technical Overview:
https://www.oasis-open.org/committees/download.php/27819/sstc-saml-tech-overview-2.0-cd-02.pdf
In the document above you will be able to find all the technical information required to analyze if SAML 2.0 suites for your scenario.
Cheers,
Filipe Santos