I have 2 queries with respect to a child portal

1)Users - Is there any setting that can simply import all the users that exist on the parent portal ? Or in other words we still have the Parent portal and a Child portal but a single set of users for the same ? The user can set his default language as EN or CN while registering. Depending on this I need to automcatically redirect him/her either to the parent portal (EN) or instead the child portal (CN) - Any suggestions or code samples on the same ?

2)Default Language - I would like to automatically set the default language for a child portal as 'Chinese'. Is this possible ? If so how do I go about it ? so what I mean here is that anytime a user gets to this site (i.e the child portal) the language 'CN' would get autocatically set - But ofcourse the user can select EN from the dropdown which is available on the header.