Multisite Domain Mapping

Hello all, I came to a situation where I need professional advice.

There is a WP Multisite installed on (domain.net) with two blogs:

domain.net/usnews (ID 2)
domain.net/uknews (ID 4)

There are two subdomains pointed to this server:

news.otherdomain.com
news.otherdomain.co.uk

This had made news.otherdomain.com AND news.otherdomain.co.uk going to domain.net. At this point it’s all correct.

Now I have installed Domain Mapping Plugin.
Network > Settings > Domain Mapping Server IP set correctly.
Network > Settings > Domains there is two domains added:

news.otherdomain.com > ID 2
news.otherdomain.co.uk > ID 4

Now at this stage we have redirect going on:
news.otherdomain.com GOES TO domain.net/usnews
news.otherdomain.co.uk GOES TO domain.net/uknews

THE PROBLEM:

How do we make visitor stay on news.otherdomain.com? At present time news.otherdomain.com redirects to domain.net/usnews. We want news.otherdomain.com/post showing same as domain.net/usnews/post. We do not want even show that domain.net/usnews exists, it should be news.otherdomain.com by default.

How do I do this?

Is it down to installing kind of plugin?
Is it down to writing .htaccess file?
Is it down to changing url in Site settings?

Thank you in advance..