How to talk to sons about sex?

Hi I'm Gina.
I'm mother of two wonderful 10 years sons. Their father has left us 8 years ago.
I have a question, maybe some of you can help me?
At what age should a parent teach their son about ‘sex’ if there is no father around or would it be better for the kid to have a male family member to do this?
It really bothers me because i've found adult magazine in their room today.
Should I talk to them by miself or ask my brother to do it?

Hope someone had the same problem and can advise me anything.
By the way, here is the photo of my sons:
www.phatcampus.com/__media__/js/netsoltr...porno.com/missionar/ - i.ibb.co/4ghm31h/main-qimg-2874a40311959...694d2f51400d8e-c.jpg