Let's just quote the whole of the paragraph :-
Please provide ten items of correspondence of the kind, or from the sources listed below, addressed to you and your spouse jointly during each of the past 2 years if they clearly show that you live together at the same address. At least 5 of these documents should be from different sources. If you have not received any such correspondence that is addressed to you and your partner jointly, it is acceptable to provide 5 or 6 items addressed to one of you and 5 or 6 items addressed to the other partner during each of the past 2 years so long as they show the same address.
I think that is unambiguous ... I think it is ten from each year. But of course not all ten need to be addressed to the two of you jointly.
Does this mean that you couldn't show a gas and electric bill if they are issued from the same company?
I think "source" here means a particular company or organisation. But look at those count rules. If one item is supplied from each of four organisations, and then the other six are from the same company .. say three electricity bills and three gas bills ... you will have supplied 10 items in total .... and from five different sources.
And all that needed for each of the two years.