If a child was born in the UK to a British or settled parent, they are automatically British.
If a child was born in the UK and at the time of their birth neither parent was British or settled in the UK, then the child is not automatically British but they may be eligible to register as British if one of the parents has subsequently become settled or British.

If a child was born outside the UK but either parent was a British citizen before the child was born, that child may be a British citizen by descent. If so, the child is entitled to apply for a British passport.

Applicants must have held ILR for 12 months before applying to Naturalise as a British citizen;
Those married to a British Citizen can apply as soon as they have ILR;
Applicants must not have been absent from the UK for more than 450 days over the last 5 years, and no more than 90 days in last 12 months before applying.
The applicant must have been physically present in the UK on the first day of their five year qualifying period at the time of submitting an application.
Children born in the UK after one or both parents have ILR are automatically British and can simply apply for a British passport.

Indefinite leave to remain (ILR) means that a migrant gets the right to live here permanently without immigration restrictions. ILR, also known as "settlement" or"settled status" will allow you and your family members to settle in the UK permanently without needing to apply for another visa to live, work, or study.
You must have lived in the UK continuously for the required qualifying period.
You are of good character
You have passed the Life in the UK test, prove your knowledge of English language at a required level, you do not have excessive absences more than 180 days outside of the UK in any year.

A Visitor visa allows individuals to travel to the United Kingdom for a temporary visit. It is designed for tourism, visiting friends or family attending business meetings or engaging in other permissible activities as a visitor.
Visitor visas are generally granted for up to 6 months. The visa allows the holder to enter the UK for the approved period. An applicant has to provide evidence of strong home ties to be successful.

A visitor visa is not intended for individuals who plan to work or settle in the UK. It does not provide the right to work or study for an extended period.

The Unmarried Partner Visa allows individuals who are in a long-term, committed relationship with a British citizen or someone with settled status in the UK (such as indefinite leave to remain) to live together in the UK without being married.

To qualify for the Unmarried Partner Visa, applicants must meet several criteria:
1. Relationship requirement
2. Financial requirement
3. Adequate accommodation;
4. English language test for an applicant
5. Some applicants may require a TB-test

A UK spouse visa is for individuals who are married to or in a civil partnership with a British citizen or a person with settled status in the UK. It allows them to live in the UK with their partner. To qualify, applicants must meet certain eligibility requirements, including demonstrating a genuine relationship, meeting financial requirements, and, in most cases, satisfying an English language requirement.

The sponsor can meet the financial requirement through various sources, including: Employment income; Self-employment income; Savings; Pension income; Non-employment income.
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A fiancée visa is for individuals who intend to marry in the UK for settlement purposes. The fiancée visa is issued for a period of 6 months. During this period the couple is expected to get married and subsequently apply for a spouse visa.

The applicant must be engaged to a British citizen or someone with indefinite leave to remain (ILR), settled status, or refugee status in the UK.
Both individuals must intend to live together permanently after marriage.
The relationship must be genuine and subsisting. The couple must intend to marry within 6 months of the visa’s issuance.

A UK Child Dependent Visa allows a child to join or remain with a parent in the UK if the parent is either a British citizen, has settled status (such as indefinite leave to remain), or holds a qualifying visa, such as a work or spouse visa.
The child must be under 18 at the time of application, although in certain cases, children over 18 can apply if they are already in the UK as a dependent.

Relationship: The child must be the biological, adopted, or stepchild of the sponsoring parent. The child should be financially and emotionally dependent on the parent and must not be leading an independent life or have a family of their own.