The easiest way to do this is to have 3 date columns. Last Meeting, Next Meeting, and Oxt Meeting. (you really only need the Last Meeting and Next Meeting column, but I like to have 3)

In Next Meeting, put the formula =[Last Meeting]@row + 7

In Oxt Meeting, put the formula =[Last Meeting]@row + 14

Create an automation that triggers when Next Meeting is reached. The automation will be to record the current date in the Last Meeting column.