I can’t comment at the moment (I haven’t got enough reputation) so I’m going to try and answer instead.
How did you set up multisite and the three sites? The subdomain URL structure would usually mean that you have a primary site (I think main.lan in your case) and then sites on the network would be a sub-domain of that site (e.g. test1.main.lan, pbtest.main.lan). I can see that define('SUBDOMAIN_INSTALL', false); is false when it should be true, and you’re right that DOMAIN_CURRENT_SITE should be a domain and not an IP address.
If you follow the process to configure multisite by going to Tools > Network Setup and selecting the sub-domains option, it should give you the necessary rules to add to your .htaccess There’s more on multisite setup here
For the three addresses, you have mentioned, to work, I think you would need to setup a site as http://lan and then have the other sites as subdomains of it.
There are ways of having any custom domain mapped to a site on a WordPress multisite network, and that might be the solution here. You used to have to use a plugin, but for some time it’s been in the core of WordPress and you can edit the ‘Site Address (URL) field’ in the network admin to the custom domain that you want to use.
I’m not confident that this has answered your question. If it has, great, but otherwise, I hope it gets you a step closer to the solution.