Your hcg levels are completely normal and doubling every 2 days in a normal manner.
There is a wide range of normal hcg levels. Your levels are higher than some and lower than others.
Fraternal twins occur when the mother ovulates 2 eggs at the same time. The fact that your husband is a fraternal twin does not increase your chance of having fraternal twins.
So I believe that your chance of having twins is about the same as for any other pregnant woman.
Congratulations on your pregnancy!
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