1- I was unable to comprehend what you are trying to say.
2- The less exercise people do, the less they live. (fewer might refer to people as fewer people!)
3- The easier parents and girls make marriages, the less single person (might) remain. (Again more parents, although you can say the more, parents... use comma to separate the meaning. Also it is not the only element in marriages' barriers, therefore I would suggest using might.)
4- Grammatically is correct. However, I do not see the connection between industrial products and hygiene...!?
5- Grammatically is correct. I would have used certificate instead of degrees. Again if one has a certificate, qualification or degree in a subject - I believe - it means that they are capable of doing tasks within that subjects unless you are trying to project the importance of experience...!?
6- The more incomes come, the more costs to pay OR the more income, the higher expenditure will be. (Again in your version you might earn more income(s) and keep the costs down or the same, so it is not definite but can be probable which I suggest the second version.)
7- ...Less and Less
8- The more we learn about the technology, the less our grandfathers might know. (remember it is not definite again as they might learn as well.)