Another Okta Org can definitely be used as the IDP for inbound SAML with an SP Org accessing it. The documentation provided below, would outline the technical topic in entirety.
If you have any issues in implementing Okta inbound SAML simply open a support ticket with us and we will be more than glad to assist in having you up and running with inbound SAML.
However, the IDP Org will be your policy provider for MFA if it is setup to require MFA for the user login from the SP Org. In other words, if the IDP Org has MFA required at the Org level, when the SP Org accesses via inbound SAML, the MFA will be prompted. Furthermore, the inbound SAML application can also be setup to require MFA when accessing it from the SP Org and this is application level MFA.
Thank you for choosing Okta!