No, not too rare. I'm part of fraternal triplets. We all look different thank goodness I don't look like a boy! Identical twins are actually more rare than fraternal twins. Fraternal twins, like any other siblings, have an extremely small chance of having the same chromosome profile.
Starting next wednesday I am babysitting an eleven year old boy whose mother I already knew. It went fine. This boy however is older and he may not like a girl checking him while he is bathing and naked. Have you ever been a babysitter for a boy this age and did you use to bath him or check him in the bath?
My 14 year old twin boys are having sex with each other!?
It all started when my sister was 8 and my brother was 5. They started sleeping together because my brother used to be afraid to sleep by himself so my parents thought it was a good idea for them to sleep together. Since then, for about a year, they would always sleep together in the same bed.