Hi Lesley,
The way to approach season planning really depends on your level of fitness, experience and goals for your A race. My initial simple suggestion given you are this far out from the event(s) would be to recommend starting the 21 week plan based on your 19th June event, thereby giving you a full general preparation plan and build leading up to that event, followed by a 1-2 week recovery/transition period where you recover and get refreshed, then re-starting the plan (and possibly even leveling up) with 11 weeks to go before your 70.3 A race. As there is more than 6 weeks between your 70.3 B event and your 70.3 A event I would be inclined to not include them in the same training block and see them as two different race builds.
Hope that is helpful.
Happy Holidays – Leyla