Have a read up on sponging etc. The numbers conceived is variable and difficult to predict based on many factors including but not restricted to bcs, whether that is rising or falling, time of year, breed of sheep, dose of PMSG, age of ewe and many more. You can give the same dose to the same ewe two years running and have different results. You judge how much to give/guess and hope for twins! It really isn't possible to give accurate advice on your flock without seeing them and their situation.... you may get a good few trips
Teasers are an integral part of many AI programmes that include sponges and PMSG