I am having difficulty in trying to convey the phrase "we both already know", as in a something which is common knowledge between the people conversing. Such as a fact which existed in the past, exists now in the present, and will continue to exist for some time in the future.

Can I use เรารู้แล้วอยู่ in that situation as a correct "we know already and are continuing to know" phrase? Also for this example consider the two people talking (one being myself) are the only ones present, which is why I didn't clarify "both" people by further designation and just left it as เรา. If I should identify the people even if it is understood by context, lemme know that as well.

I'm trying to get this language usage/structure right, but it is an uphill slog.

I would try something like "ก็รู้กันอยู่แล้ว".