I have 2 sons i aged 11 and another son aged 7 years .

I want to know whether i can conduct upanayanam for the 2 sons simultaneaously? as i had mixed response that it is not advisible to perform upanayana for both sons as there is a ritual called hair cut for both. iam confused in this answer kindly
tell me what our sacared books tells us

I also want to know what is the right age to perform upanayana.

ganesh