Though allowed I would not check cremains, carry them on in a fully seal bag that it is clearly marked cremains with a copy of the death cert. Here are Delta's and the TSA policies:

https://www.deltacargo.com/ProductsR...anRemains.aspx

http://blog.tsa.gov/2012/06/travelin...y-remains.html

IME, it was not an issue to carry my FIL on board in a simple wood box, he was appropriately bagged and tagged (sorry black humor). The TSA did not take a second look at our carry on.

Good luck and may you celebrate their life with a smile.