User connecting to AX thru VPN client

Dear All,

AX version: AX 2012 r3 CU10

Database : SQL Server 2014 standard

Scenario:

Domain name in one country is  "A.uk"

AX Database and AX AOS installed under domain A

Domain name in other country is "B.us"

Question-1:

Now users from domain B wants to access the AX thru VPN.

Since the users added in Ax only for domain A users.  How can domain B users can access the AX thru VPN.

Question-2:

Also, if my company has two domains in one location. In that case can I able to select/add the users in AX from both the domains  for them to access.

Thanks & Regards