I would suspect the nap is too long. My 20 month old is on a very similar routine, just with a 1/2 h earlier bedtime. My oldest was on no naps by 2.5 (with a 12 hour night) and I consider both of them fairly average for sleep needs. Also, could he be uncomfortable in his crib? Though I can imagine it is much easier to keep him in it if you also have twins, maybe he is ready for a BBB?
HTH
Heidi