I'm not in the dairy game but from what I've seen of it from afar, it seems akin to a vocation to join the priesthood. If you have ability to keep 84 milking cows, some calves, plus in calf heifers, then I'm making the assumption that you've got a decent plot(s) of land to start with.
I agree with
@Mf310 that option 1 is not giving you any tangible benefit - there is no step change from where you are now. So, you can rule that one out.
You've already ruled out option 2 yourself. How many heifers would you have so a second opinion can be given on this? Would this plus OAD milking give you any relief?
3rd option is a decent one.
If you opted for the 3rd option could you run anything alongside it? Would you get sufficient number of heifers to fully utilise your land? A nice mix would be to get a part time job, some heifers to contract raise and maybe do some round bales to sell on later in year and a few drystock of your own to keep the cashflow coming in throughout the year. You could still even do some relief milking out and about to keep the hand in and get experience with other systems in order to see if you hate milking or hate your setup!
If you went P/T do you have any type of job/career in your mind that you want to do or are qualified to do?
I'd avoid renting as it is a nuclear option and from anyone I've seen who done it not another member of the family owned a hoof on the land again.
Edit: I should add to this, are you able to determine the difference in income if you were to reduce numbers, drop milking or start contract rearing? Would it be viable? I would have thought that folk on here could give an estimate of the income available for contract rearing heifers.
Thinking about this a bit more, if this was me, and I appreciate that it is not, I would work on a sliding scale of changes until I reached a suitable balance.
i.e.
1. Maintain current herd and switch to OAD
2. No improvement. Reduce herd to a smaller number of milking cows and contract heifers. Maintain OAD (depending on successfulness within step 1.)
3. Still not happy. Exit milk production and enter contract rearing, plus sideline activities to bridge income shortfall
Might take a bit of time to get to your balance point, but no point going all in on something without trying all the options. Sometimes just changing something can give you a bit of heart and renewed vigour for it all.