Hiya!
Sorry not tried mixed feeding, and I'd be wary of it doing things to the supply but that's fine if you want to go down that road particularly at this age. You have done so well already.
I just wanted to suggest a couple of things - probably not much help but anyroad.
I have a 9mo and the waking is kind of random - sometimes he sleeps really well, other nights he seems to have a lot of wind, so he is restless, especially towards morning - also he was unsettled when he was getting his first teeth, so it could well be that.
I also co sleep and can't imagine doing otherwise as you're there immediately with them to sort it out, whatever it is. So no advice on that front except you don't have to stop, you can carry on as long as you wish.
I agree totally on taking the line of least resistance - this is my third child, the other two sleep happily in their own beds, now - it isn't an issue that they will never leave if you let them sleep next to you. I actually think it makes them MORE secure.
Please ignore your family and HV on this - obviously DH should get some input! But still, I don't think any of their suggestions is going to get you a result. It's just a generalised distrust of the natural way of doing things, many cultures (Japan I think is a good one - very modern) co sleep and so on as a way of life. You need backup to make them see sense. Or you can just carry on as you are.
Good luck and don't worry, your ideas are right, as far as I can see, and they are just panicking because they know there is an alternative, (and think it might stop all the issues) but the problem is, it isn't a better one - this is just what babies DO and it doesn't mean you're getting it wrong.
It is v hard going against your family, I know.