Originally Posted by
LastViking
I am sure you will get a more informative reply from those others on the site. For my part I think it is a matter of logic. Will your joint incomes in the UK be enough for you to live on without recourse to public funds. That must be the test.
If you have enough income with your wife's job offer to cover your costs of living but only just and your parents in law are prepared and able to help, then I would get a letter from them to support your application. Bear in mind that until you are married and your wife has a spouse visa, your fiancee will not be allowed to work in the UK on a fiancee visa.
If you do need your parents in law help, they would have to able to demonstrate that they have excess income available. If they are supporting other family members, UK immigration will be doubtful. What evidence could they or would they be prepared to supply in support of your application?