If you take birth control regularly, miss one does on the only night you've had sex in 1 year (no sex after), then continue to take regularly thereafter, how is it possible to get pregnant with twins?

Nothing perfect: Not only that, but since you aren't the person who claims they only missed one pill, it may not really be true. It is possible, although unlikely, to become pregnant without missing a pill, so do not be overly surprised. Sounds as if you might want dna confirmation if she claims you as the father.

Bcp's are not 100% : When l was training 40 yrs ago bcp's only claimed to be 99% effective. Since then they have reduced some of the doses of the hormones and they must be taken at the same time every day to keep the levels to prevent pregnancy. I feel for you, but some babies are just robust and need to be born. Good luck. I hope you find the love all of you need.