Greetings Beryl,
You could go for a development as suggests. But then you will have to develop the specific logic.
You could also maybe get some good results using a Strategy and Offsets. Please could you look at the thread here Scheduling plan - Every two months, the third Friday where I tried to tackle a similar issue.
One possibility that comes to mind is to use a weekly Strategy and Offsets. Make sure you align to the beginning of the week (Sunday, Monday etc. depending on your local convention... I'll assume Monday in my example) for your cycle start dates. Then create relevant packages.
Offset the Tuesday package by 1 day. Offset the Wednesday package by 2 days. Offset the Sunday package by 6 days. Offset the fortnightly package by 5 days. You get the idea...
Note that since you'd need to offset by a set number of days, you can't use the WK "Week" unit for your Strategy. Use Days instead and multiply by 7.
See the attached screenshot for a worked example. This would let you plan in a weekly, bi-weekly, four-weekly, and twelve-weekly cycles, and fine-tune the Operations that would fall in those particular Package frequencies. Note however, that 4 weeks in this case <> 1 month and you can't use the key date scheduling. See in the example where I schedule from 1st September 2014 (which is a Monday), the "1st Wednesday" Package falls out of place as soon as 29.10.2014, which is the last (5th) Wednesday of October.
So if you wanted to keep to the monthly cycle more strictly, it would become more complicated to achieve your objective using Strategies alone (the solution might then be similar to Jerome's, but since you are looking for a weekly precision, not bi-monthly, it would probably be too convoluted to implement for a reasonable scheduling period (such as >1 year)
Let me know if this meets any of your requirements, or perhaps we can look into this further! 