Thank you. I am sorry to hear about this matter. In the first case you will want to look at the house deeds to see if you actually have ownership of the pathway or just the right to use. You will also want to check who has responsibly for the maintenance of this and if the own the half they amended. This will provide information about rights. If they did not have the right to do this, you could look. t obtaining an order to have this amended. In terms of their extension, I cannot confirm however, it is likely they would have required planning permission, if this is on their land the it likely they would have had the right to build it this way.
I shall provide you with a helpful link that will assist you in finding a solicitor/representative near your local area. This will provide you with someone nearby your area who can assist you if required.
I hope this information proved helpful. You will find a local solicitor who deals with these matters on the law society webpage which is as follows;
https://www.lawsoc-ni.org/solicitors (N. Ireland)
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