If you each earn more than £18,600 individually, then you should not provide evidence of both incomes - because they only need to see that one of you earns the minimum amount.
By providing two sets of financial documents - one for each of you - you end up complicating the application (by giving them twice as much financial paperwork than necessary to go through) and you increase the chances of making a small mistake with the documents which could potentially lead to a refusal (i.e. if one set of financial documents meets the formatting requirements but the other set doesn't).
So, best thing to do is decide between you which of your incomes is easiest to show in terms of providing the correct documents and then only include the employment details for that person... and leave the employment details of the other person blank on the application form.
For example, if one of you receives paper payslips and/or bank statements and the other receives electronic payslips and/or bank statements, then it may be best to use the income with the paper payslips/statements. Or if it's easier for one of you to get a letter from your employer than the other. Or maybe if one of your incomes is more straightforward to show than the other (i.e. fixed annual salary vs. non-salaried or variable income). Or if one of you is employed and the other is self-employed, it's much, much easier to meet the requirements using employment income than self-employment income.
