There is no way to you make yourself conceive twin boys. Firstly - you're highly unlikely to conceive twins naturally unless they run in your family. Secondly - there is no way to make sure you conceive a particular sex. That depends on whether a male or female sperm fertilises the egg - and since millions of sperm are released with each ejaculation then there is no way to know or ensure a certain sperm fertilises an egg.
Few medical facilities will do gender selection unless there is a disability or chromosomal disorder associated with one gender offspring.