Congratulations on the twins!!!
As an infectious disease nurse, I whole heartily agree that they should be washed and dried with hot water and heat to kill the yeast, molds, viruses, and of course the bacteria. Those premature immune system has not fully formed yet as many of the immuneties from mom are given at or near term delivery.
The quilts are made with 100% cotton and batting so not to worry. ALL of the quilts in the NICU's across the USA are washed in hot water. You might want to consider a softer color rather than the bright reds, blues, or greens.
Enjoy the little ones and be confident in the staff to do right by your precious twins. Thanks for asking.
Karen