Travelling to ROI via NI from UK mainland

Hi guys,
Hope some of you can shed a light on this.
I tried looking at some other topics open on here but I couldn't find a similar and recent case.

We are planning to travel from UK mainland to NI (Belfast) and stay there for two nights. I can see on the various government websites that for now there is no quarantine measures in place. 
We were planning to cross the border and go to Ireland but I have seen that if you are crossing the border from NI to ROI you are exempt from quarantine but if you are coming from a country not on the ROI green list (UK isn't on there) you have to quarantine for 14 days. 
 
So my main question is can we cross the border without self quarantining as we are coming from NI or we need to self isolate? 
Eventually is there any form that needs to be filled out online or the location one is just for people arriving via plane/ferry from overseas directly to ROI?
Do you guys have any dates on when there might be another update on this? Does this gets updated every two weeks? 

Thank you!

Hi Matteo,

We can completely understand the seemingly confusing information about travel in these times and hopefully, I can clear up any ambiguity. 

Things are evolving periodically regarding travel both to and from the island of Ireland as well as on the island of Ireland. There is indeed, no quarantine in place for individuals travelling to Northern Ireland from mainland Britain but the UK government is still advising that you should avoid all non-essential travel. 

There is no border control between Northern Ireland and the Republic of Ireland, so residents on the island of Ireland are free to travel anywhere on the island of Ireland without the need to restrict their movements. Again, non-essential travel should be avoided. 

All international visitors, including those from mainland Britain who are arriving into Northern Ireland and then travelling into the Republic of Ireland are still required to fill in a passenger locator form and expected to restrict their movements for up to 14 days as well as some other safety precautions if not on the green list countries that was updated on the 5th of August for the following two-week period. This is under constant review and changes to this are occurring at planned intervals as the situation allows. Currently, the passenger locator form needs to be filled in and emailed to this email address if you are not coming into the state directly, it is planned to be online soon. passengerlocatorform@plf.ie

Please continue to check the official websites for more details, links available on our travel health page and GOV.IE page where all of the official updates are provided.

Hopefully, this helps try to explain the situation.

Please feel free to come back and ask any further questions,

Martin