Hi Bird,
I had SPD with both of my DC( crutches, support belts (day and night) painkillers) turning over in bed, getting out of a chair felt like I was 90)which was pretty awful. But it doesn't compare with you:
You are heavily pregnant (with all the aches/pains/ worries/stresses/hormonal feelings that that brings in itself)
You are in pain, probably 24/7 from dreadful SPD even while in bed and are on crutches. Your sleep will be very disturbed.
You have a 4 year old at school- school runs/hours.
A toddler around ?all day who you are having to entertain/ stop injuring themselves.
A husband who is away a couple of times a week
Step children + 4 year old + 21 month old + a husband who wants to leave you with them for the day.
It is likely that you are isolated as you cant even pop out for a pint of milk/quick chat/ interaction with other people without being in agony/ having to lift/ walk with a toddler (concerns about them running off if you cant run after them if they run into road etc) when you are on crutches and possibly feeling guilty about asking for the school run and other favours.
Bloody hell
at all the above. Would your other half do the same if he had broken his leg and was on crutches and you were away a couple of times a week, leaving all the childcare to them? I think not. Explain it in those terms to him. If he doesn't understand show him your post.
You need support. Call in ALL favours/friends/ family help. This is hopefully only for another month or so. Your OH needs to up the help even if he is helping/ trying it just isn't you its the whole family. If he can go to a football match all day he can give you a time to breathe/ rest all day and take the kids out/look after them. sure he is also tired etc but that doesn't mean you have to do it all.
Ask to speak to a midwife supervisor at your hospital on the phone due to your mobility issues who can discuss the induction date/ your situation if they are being strict with dates. Yes there are medical reasons babies shouldn't be induced early but they need to know how bad you are. I have met quite a few people over the years since I had my DC (last 6 years ago) to know that this sort of pain/ isolation will mean you are prone to postnatal, even antenatal depression.
Hugs, hugs, hugs, hugs.