Genetic testing- people who have had or are going through this

Hi, 

I am wanting to get as much information as possible. To give you abit of a back story to my reasonings of wanting to be referred for genetic counselling... 

My close family has got a very strong history of cancer and unfortunately deaths caused by cancer. 

This is all on my maternal mothers side of the family.

My Mother's maternal grandmother-lung cancer died at 60

My Mother's Maternal Mother- firstly breast cancer/thyroid cancer in her 30's in remission all clear and then lung cancer 64 died 66

My Mother's brother- bowel cancer diagnosed 39 died 40

My Mother's brother- lung cancer spread to liver died 43

My Mother's sister- lung cancer, spread to ovaries, stomach and brain died 49

My Mother's daughter (my biological sister)- kidney cancer diagnosed 33 now 38 spread to her lungs, bones and brain. Still alive. 

This is a strong history of cancer in my family. I have two young children. I am getting concerned that this may be a gene mutation that has been inherited. I am worried that I may carry this gene and that there's a possibility that my siblings and my children may also have these genes passed onto them. I am worried that my doctor will dismiss this. I have spoken to them about my concerns in the pass and I have been told not to worry. Cancer at young ages are unheard of and not that common. (In my case this us so untrue) 

I would like to have genetic testing and I would like to know what happens if I am found to have the gene mutation? And advice. I have researched the process and the counselling involved etc. I just want peace of mind for myself, my children and my siblings. Any help and advise would be greatly appreciated.