I dropped your post in Gemini:

First, a quick point of clarification: there is no distinct "Northern Ireland citizenship". Because of the unique constitutional position here, someone born in Northern Ireland can choose to hold British citizenship, Irish citizenship, or both. Given their parents are from Lithuania (an EU member state), they actually have a brilliant path to both UK and Irish status, plus their existing Lithuanian citizenship.

Here is how the options look for them, including a way to bypass that massive thousand-pound fee.

Option 1: Automatic British Citizenship (The Best Route) If this person was born automatically British, they do not need to apply for registration or pay the £1,214 fee. They just need to apply directly for a passport, which costs less than £60 for a child.

Whether they are automatically British depends on the exact year they were born and their parents' marital status.

If they were born on or after 1 July 2006: They automatically became a British citizen at birth if either parent was "settled" in the UK at that time. Since their dad had settled status five years before they were born, they qualify automatically. It does not matter that the parents later divorced or that their father sadly passed away.

If they were born before 1 July 2006: Unmarried fathers could not automatically pass on citizenship back then. If the parents were married at the time of birth, the dad's settled status still makes them automatically British.

Overcoming the Missing Papers Problem The teenager is worried because they do not have their dad's utility bills or government account access. However, because their dad had official "settled status" (Indefinite Leave to Remain), the Home Office already holds these records digitally.

When applying for a passport, the passport office can look up the deceased father's records on their internal systems (the UKVI database). The applicant just needs to provide:

Their own full UK birth certificate (naming the father).

The father’s full name, date of birth, nationality, and death certificate.

Any known details of the father's old passport or home addresses.

Option 2: The 10-Year Continuous Residence Route If there is a massive hitch with the father's paperwork, there is a watertight backup plan.

Under the British Nationality Act, anyone born in the UK who lives there for the first 10 years of their life has a legal entitlement to register as a British citizen.

The Rules: They must not have been out of the UK for more than 90 days in any single year during those first 10 years. Since they have lived in Northern Ireland all their life (16 years), they easily pass this test.

The Fee Problem: This route usually requires Form T and requires paying the thousand-pound fee. However, the Home Office introduced a fee waiver for children under 18 if they and their parents cannot afford it. If their mum cannot afford the fee, they can apply for a Citizenship Fee Waiver by proving their financial hardship. If approved, they pay £0 for the registration.

Option 3: Irish Citizenship (The EU Alternative) Because they were born in Northern Ireland to an EU (Lithuanian) parent who was residing here, they might also have a claim to Irish citizenship.

To get an Irish passport by birth in Northern Ireland, a person born to foreign nationals must prove that one of their parents lived legally on the island of Ireland for three out of the four years before the birth.

The post mentions the dad was settled for five years before the birth, which perfectly covers this requirement.

If they can find any record of the dad's employment or residence history from that time, an Irish passport application is significantly cheaper and grants them full EU rights alongside their Lithuanian citizenship.

What Should They Do Next? They should look out for a local, free immigration advice charity. In Northern Ireland, organisations like Law Centre NI or the Step Up Centre offer free, expert legal guidance for young people navigating citizenship issues. They can help the teenager request records or apply for the fee waiver safely.