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Hello there, How can I help?
Where is she currently located
Does your daughter have a good knowledge of English
Will the marriage take place within six months of arrival in the UK if the visa is granted
Is their combined income above £18,600
Suitable evidence to show a genuine and subsisting relationship
If the couple has been living apart for a lengthy period of time, or have never lived together, prior to submitting a spouse visa application, suitable evidence of a genuine and subsisting relationship could include, for example:
You don't need to ask because it's their combine income.
https://www.gov.uk is where you need to go to apply from your country online.
I do hope this helps. Please don't forget to rate my answer to close the question, this ensures I'm compensated for my time if you're satisfied. You can, of course, ask additional questions afterwards too.
It really depends, there may be additional questions of checks if there are issues with documents etc, if everything is in order, it should take about three months.