could be .... bear in mind that originally it is خليل مأمون
And these are all transliterations from Arabic to English which have no specific rule. for example my name is Ahmad but some people write it Ahmed ..... Khalil could be written Khaleel and Maamoun could be Mamoon, Mamoun, Maamoon, Maamoun ... etc. as long as it is phonetically same/similar to the Arabic pronounciation. Got it?