Split Fibre or get another one at the same address.

[gg30340]

Why would power line adaptors not work? Perhaps the set you have previously used were not up to the job.

EDIT: It sounds like you are set on getting a second line, which has already been pointed out would probably necessitate drilling holes plus the additional cost of the second line.

If you are going to get holes drilled in any event, getting an electrician to do the work of installing an Ethernet cable would probably work out a lot cheaper than the on going monthly cost of a second line. 

[Dominix]

Packet losses.
That's something I will try, but that's why I'm asking now, to know what to do if this will not work as needed. It's not gonna be for web browsing or yt. It has to be stable connection all the time.

[verkosh]

Ethernet itself shouldn't have packet loss.

And it's good for runs of up to 100 metres. You can also get outdoor grade capable ethernet cable 

[Dominix]

Ethernet cable, yes, shouldn't have. But power line can, as if your electric circuit is bad or bad quality, that's why I'm not fan of it .

[iniltous]

As stated , if cost is only a secondary concern, a second FTTP service should fit the bill , but you need to ensure that your new ISP ( or BT if you intend to use BT for both services ) understand the need for a completely new service, there is also a ( probably less likely ) chance that , as addresses are only allocated a single port on a CBT at the design stage , if FTTP take up has been strong , there may not be a spare port on the CBT , and a second service delivered by changing your existing ONT from a single port to a multi port ONT , you would have 2 services, but at the same location, in which case your cabling issues still exist , but this is very unlikely.

[Dominix]

I'll will start with this, call BT or other provider, it doesn't matter who, and see if they can do it. If yes, then I will try something else like powerline adapter, if it will fail, will probably get another line. At least now i know what I can do.