I am the one who throws a spanner in the works and will suggest a much shorter A time :-) My 14MO copes really well on a 30-40min capped morning nap at 9:30am, longer nap at 1:30pm (usually about 1.5hr and I cap at 2hr) and BT at 7pm. So her A time is actually never more than about 3.5hrs - goes against a lot of the advice you read about typical A times but it works really well for her and I personally know a lot of kids her age who also still have a morning and an afternoon nap. She wakes around 6:30am but I put her down at the same times regardless.
I know it's conventional wisdom that an earlier morning nap leads to EW, but I have personally found a later pm nap leads to EW and even when she sleeps til 7am I still put her down at 9:30am and it never causes EW. OT can also lead to EW and to me it sounds like your little man is OT. Just an idea and I know that probably doesn't work at all with your DD's routine (unless she is flexible enough to change to her brother's routine). Hats off to you for getting through a year with twins! Anyway I'm sure you'll read lots of different things, so good luck, hopefully one of the suggestions is right for your family :-)