For me, 4-6 months was REALLY tough, because I made myself crazy about napping or their lack their of. My guess is you wont have that issue, since you have other children and know that there's little you can do to actually make them sleep 
It is really fun right no (almost 21 months), so active and talking. But, yes, I agree, two at once is well worth the craziness.
Also, I just read this book that I found wonderful, One and the Same: My Life as an Identical Twin and What I've Learned About Everyone's Struggle to Be Singular by Abigail Pogrebin. It was really interesting to see all of these facets of "twinships" that I had never thought of before. I really recommend it.

It is really fun right no (almost 21 months), so active and talking. But, yes, I agree, two at once is well worth the craziness.
Also, I just read this book that I found wonderful, One and the Same: My Life as an Identical Twin and What I've Learned About Everyone's Struggle to Be Singular by Abigail Pogrebin. It was really interesting to see all of these facets of "twinships" that I had never thought of before. I really recommend it.

