what are my odds of having twins if I have them in my family?

I am the second oldest of 11 children there are 10 girls and 1 boy. I am not a twin but I have 2 sets of twin sisters, they are numbers 3 & 4 and 10 & 11 both fraternal. these are the only twins in my family. I do have endometriosis which was diagnosed a few years back through a laparoscopy. They burned out what they could it was mainly around my ovaries, there was also a lot of scaring. I also have vaginismus. We have been trying to conceive since January 09 and so far we have had no luck. I have been tracking my ovulation with a menstrual calender as well as tracking my BBT. My cycle lasts 35-36 days my period is only 1 to 2 days long usually heavy on day 1 and light to nonexistent on day 2 with clots. according to my BBT some months I ovulate but others I do not. I take folic acid everyday and I have a little weight on me (my BMI is 32). My husband and I really wanted twins (not to just get it over with we just LOVE twins) and I am going nuts trying to figure out why we haven't conceived. my ob said if we still haven't conceived in a few more months then we'll do a 21 day progesterone and an HSG. Is there anything we can do to get pregnant now I would love twins but right now i'll be happy with just one. Considering the issues are my chances of twins lower even though my mom has two sets of twins?