Visas, Civil Unions and naturalisation???

Hi all, my name is Em and I'm currently in Cambodia but looking for kind of complicated information.

I live here with my partner and 2 kids and we're looking into moving permanently to Malta in the next year or two.

Here's the catch: As a UK citizen I don't have issues with visas/residence etc, however my partner and kids who are Cambodian would like to eventually gain citizenship by naturalisation. Of course they will need residence first. So I have 3 main questions:

1. Is it really as easy to get visas and then residence in Malta for non-EU citizens? I read on numerous websites that you can come into Malta on a tourist visa and then apply for residence while you're there. However in a couple of places the info is different. I'm hoping someone can clarify this so I have the right info. And when residence is gained, does it allow ease of travel within the Schengen zone to non-EU citizens or does that rely solely on their actual citizenship?

2. Has anyone formed a civil union with a non-EU citizen in Malta? Again, many sites seem to say this is very easy but I'm not 100% sure. In Cambodia, same-sex relationships are not recognised so we would like to form a civil union abroad.

3. Does anyone have experience as a non-EU citizen gaining citizenship by naturalisation? I know that you must be a resident for minimum of 5 years, but are we going to get that far only to find that it's not possible after all?

Sorry for such a long post and so many questions. I'd appreciate if you can give any relevant information whatsoever on any of my questions.

Cheers!