Hi both can I be cheeky and offer a bit of physio advice for labour and SPD? Sorry if you know this already....
If you labour without an epidural then you'll still feel your SPD pain and this will guide you as to the best positions to stay in during labour.
But if you have an epidural you won't feel your SPD pain any longer and this can actually cause more problems.
Because you can't feel the pain anymore some women end up getting into positions which put more strain on your SP - things like lying on your back with your legs open, squatting with your knees open wide or the worst of all using stirrups / pushing feet against resistance.
Then when the epidural wears off you've wound up doing further damage to the SP and when the pain should reduce from having the weight of the baby gone you're actually worse off.
I've been called to see countless women who've ended up in this situation following an epidural and it's so hard for them because they expect the pain to have gone and they also now have a baby to look after - and crutches and a newborn don't really go together!!

I know you're both planning hypnobirthing so hopefully neither of you will need an epidural but just in case you do end up having one.... make sure your midwives / nurses / OBs remember your SPD and take it into account even when you're numb. If you get pain on opening your legs then beforehand measure with a tape measure how far you can open your legs before the pain comes on then you can tell your health care providers how far they can open your legs with an epidural in place.
Hope that helps and sorry again if you know all this! In the meantime keep your legs together, always stand equally on both legs and make sure you're fully supported with pillows under knees and bumps in bed