Merging two NT4 domains

Two companies having their own separate (NT4) domains “A” and “B” were merged together. We created new users, some with the same name on both domains but with different shares and rights. Later on we established two way trusts between both of the domains, now we have decided to merge both domains.

I am very confused and need help.
How can I merge two Domains? There is no Windows 2000, NT4 environment only.
How can I move users to other domain where the same name with different rights exists?
Does any one have experience doing it?

Would appreciate any help in this regards,
Thank you,