Something or someone that can be compared to something or someone else, but is not as good is a poor man's version; a writer who uses lots of puns but isn't very funny would be a poor man's Oscar Wilde.
This idiom means that determination is often more important than size, strength, or ability. ('It's not the size of the dog in the fight, it's the size of the fight in the dog.' is also used.)
From 'Robinson Crusoe', a 'Man Friday' refers to an assistant or companion, usually a capable one. The common feminine equivalent is 'Girl Friday'. (Also, 'right-hand man'. )
(USA) A mom and pop business is a small business, especially if it is run by members of a family. It can used in a wider sense to mean that something is small scale.
If you say that you are not your brother's keeper, it means that you are not responsible for someone or what happens to them as a consequence of their actions.
If a characteristic runs in the family, it can clearly be seen members of different generations. A hereditary illness that is passed from one generation to the next also runs in the family.
A straw man is a weak argument that is easily defeated. It can also be a person who is used as to give an illegal or inappropriate activity an appearance of respectability.