Apex domains cannot have CNAME records.
Question and response
Question
dig myourtheir.com. NS
Answer
myourtheir.com. 5 NS ns2.myourtheir.com.
myourtheir.com. 5 NS ns1.myourtheir.com.
Authority
The response has no authority records.
Additional
ns1.myourtheir.com. 5 A 173.44.187.162
ns2.myourtheir.com. 5 A 5.135.31.99
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0