sorry I cannot give advice on how to concieve twin boys but I know it is possible for you to have twins because it is genetic and my grandmother had a set of twins, a boy and a girl. and my twin aunt had 2 sets of twins!!
Fraternal twins can be either same gender or different gender... my nan had fraternal twins and she had a girl and a boy...
Boy sperm are faster but don't live as long as girl sperm so have sex only on the day of ovulation and the day after. Best bet would be to use the ovulation kits and when you get a positive have sex on that day and the day after. As far as twins, it's a hormonal thing i think.... lots of women in their older years (later 30's) have twins because for some reason as you get older you drop more than one egg at once.
You should check out the Shettle's method, which supposedly can be used for gender selection. I was reading about this recently and it said that (naturally conceived) fraternal twins are almost always the same gender and it has to do with the timing of BD with respect to ovulation. It also said that gender can also have to do with health and exposure to toxins of the father. Apparently boy sperm are much more fragile, so men with high toxin exposure or health issues tend to primarily have daughters bc their boy sperm are not strong enough.
since most of the people on here are struggling with having any children at all, i don't think you will get a ton of sympathy trying to not only gender select, but specifically twins...
if you are a twin, then you may be more likely to ovulate more than one egg at a time (and have fraternal twins) but i know of no way to "increase your chances" aside from subjecting yourself to IVF.
be happy with your 3 girls and if you are meant to have twin boys, you will.
I have the 'twin gene' in my family also... twins generally carry in the womans genetic bloodline because the woman carries the gene to ovulate more than one egg a month... and that gene is passed on to her children... it is carried in boys and passed on to their daughters.... there is the chance that you may have twins, but for no scientific reason it does tend to 'skip' a generation...
my mothers mother had twins... (my nan) but my mum didnt, and neither did her sisters... but my cousin is now having twins... weird huh?
If you are meant to have twins then you will, but I have never heard of it to not skip a generation... sorry hun xx