1.I have three brothers.
My brother who lives in Sidney came to see me last month.
My brother, who lives in Sidney, came to see me last month
2.I have one sister.
My sister who is 25 years old spent her holiday in France.
My sister, who is 25 years old, spent her holiday in France.
3.Bob's mum has lost her keys.
Bob's mum who is a musician has lost her car keys.
Bob's mum, who is a musician, has lost her car keys.
4.My friend Jane moved to Canada.
My friend Jane whose husband is Canadian moved to Canada last week.
My friend Jane, whose husband is Canadian, moved to Canada last week.
5.I am a shoe fanatic.
The shoes which I bought yesterday are very comfortable.
The shoes, which I bought yesterday, are very comfortable.
6.Mr Robinson is very famous.
Mr Robinson whom I met at the trade fair is a famous inventor.
Mr Robinson, whom I met at the trade fair, is a famous inventor
7.Tamara has two cats. Both of them are black.
Tamara's two cats which can play outside are black.
Tamara's two cats, which can play outside, are black.
8.Kevin has four cats. Two of them are black.
Kevin's two cats which are black can play outside.
Kevin's two cats, which are black, can play outside.
9.We are on holiday. Yesterday we visited a church.
The church which we visited yesterday is very old.
The church, which we visited yesterday, is very old.
10.We are on holiday. Yesterday we visited a church.
St. Mary's Church which we visited yesterday is very old.
St. Mary's Church, which we visited yesterday, is very old​

Defining & Non-Defining Relative Clauses:

1 I have three brothers.

Уточнение об 1 брате из Сиднея, без запятых:

My brother who lives in Sydney came to see me last month.

2. Дополнительная информация о возрасте единственной сестры: с запятыми

My sister, who is 25 years old, spent her holiday in France.

3. Дополнительная инфо о профессии его мамы: с запятыми:

Bob's mum, who is a musician, has lost her car keys.

4. Дополнительная: с запятыми:

My friend Jane, whose husband is Canadian, moved to Canada last week.

5. Уточняющая: именно эти туфли!

Без запятых

The shoes which I bought yesterday are very comfortable.

6. Дополнительная: с запятыми

Mr Robinson, whom I met at the trade fair, is a famous inventor.

7.Tamara has two cats. Both of them are black. Дополнительная информация: что 2 кошки и обе черные: с запятыми

Tamara's two cats, which can play outside, are black.

8.Kevin has four cats. Two of them are black. Уточняющая информация: 4 кота, но именно 2 играют на улице:

Без запятых

Kevin's two cats which are black can play outside.

9.We are on holiday. Yesterday we visited a church. Уточняющая информация: именно эта церковь старая, которую мы посетили: без запятых

The church which we visited yesterday is very old.

10.We are on holiday. Yesterday we visited a church. Дополнительная информация: с запятыми

St. Mary's Church, which we visited yesterday, is very old.

!!! Обычно запятыми обособляем дополнительную, НЕ важную информацию. Если эту часть предложения опустить, то предложение выражает законченную мысль: номер 2: My sister spent her holiday in France. Кстати, ей 25 - значит, запятые и просто дополнительная информация. (Если бы у него было 2 сестры, и говорил именно о той, которой 25, и она побывала во Франции, то тогда было бы без запятых, как в номере 1 про брата).