You're not a failure at all. Every body is different and muscles have different strengths and weaknesses. It might be that your pelvis or the way your muscles have worked over the years mean that a back to back position is more likely for your babies. Day to day that pelvis and muscle set up works just fine- it supports you and your growing baby, helps you get places and does every you ask of it. But in this one small area, tiny, really, compared with all the hours you're alive, it might just not work quite as it should, or could. And it's disappointing, but not something you can control and definitely not a reflection on your or your body's amazing ability to grow and produce a baby from scratch.
It may also just be bad luck to have it twice in a row. Back to back is super hard to push out and pushing for 2.5 hours is really hard core- you are a tough cookie, well done!!
Hypnobirthing is incredible and super helpful for many women, but there is variety in teachings and sometimes it can make things harder for first time mums. Most women have a strong urge to push and bear down when it's time. Some strains of hypnobirthing argue against pushing and encourage you just to breathe your baby down. As you've read above, that can actually work for some people, especially if it's not their first baby and their muscles have birthed a baby before.
But the first baby is quite often the hardest to birth because your pelvic floor is stretching and moving in a way it never has before. Going back to that particular strain of hypnobirthing, I always find it very strange that their philosophy seems to be to "listen to your body, trust it and go with it. Apart from when it tells you to push. That's wrong- you need to ignore your body and then try to breathe through these incredibly powerful urges to birth your baby". It just doesn't match up for me and sometimes it does seem to make things harder because pushing out a baby can take a while and is hard work, especially if it's your first.
But, in summary, it sounds like you have tried everything you could both times and you should be really proud of your strength in trying. Back to back is hard. It might happen again with this baby, but it might not. Either way, all you can do is your best. Eat snacks, stay hydrated and let gravity help. You've got this xxx