OE'M, join the huge MDC club. There are a lot of us here who are/have tandem nursed.
DS#1 weaned at 3 and had tandemed with his little sister DD for one year at that point, and when my DD weaned this summer at 3.5, her baby brother was 16mo. And am now anticipating another (iy'H) go-round with tandem nursing ...
If you dig around this forum (Extended Breastfeeding) you'll find a whole bunch of threads about it, and I'm always game for a new one ...
Remembering the days before my second was born and I was anticipating nursing two, didn't know anyone real or on-line who was doing it, and feeling kind of freaky ... well, finding MDC and similarly-situated mamas was a big relief.
Glad to have you round these parts ...