The chances of finding a double yolk egg in a carton of eggs are about 1 in every 1000 eggs.
Zygote
Yes it is still possible but it reduces the chances of it occurring
It takes around 60 days from conception to laying eggs.
having lots of intercourse on yor fertile days
Chickens mate by the rooster mounting the hen and transferring sperm to fertilize her eggs. This typically involves a short mating dance and can happen multiple times in a day to increase the chances of successful fertilization.
Multiple EGGS are layed but not all survive.
Low
There is a good chance.
It is possible to have multiple sets of multiples, and giving birth to multiples can also skip a generation. Hyper ovulation (the tendency to release multiple eggs during ovulation, increasing the chances of conceiving fraternal twins) is a factor in giving birth to twins.
This shouldn't affect your chances of conceiving. Just remember not to do this once you are pregnant.
It only takes one to do the job. The chances go down, but it can still happen.