8m!! Mwahahaha! Would love to know what your HV would say about my 23m who woke at 11, 12.30 and 4.17 last night!
I saw my HV when DC1 wasn't sleeping through at 10m. She grinned and said "welcome to parenthood. Learning to talk will stop them sleeping through, so will learning to walk, so will making friends, so will potty-training. Next thing you know, they're teenagers and they won't go to bed till 4am!". It wasn't exactly practical advice but it helped to know that a) the DC are perfectly normal, b) HV is right and just when you think you've cracked it, sth else will upset the sleep pattern (DC2 has yet another cold), c) your life never goes back to how it was pre-DC, so you need to start thinking in a different way ("woke only three times last night? Woohoo!"!).
For us, it was finding a pattern that works. We do shifts - I stay up later than DH, try to get the house cleared up and basically hang on till DC2 invariably wakes 11-12ish. If I can get in there at the first sign of stirring, I can stop him waking fully. This worked for DC1 and for both DC in terms of getting naps to last longer than 20 or 40 mins. It's getting better for us, quite frequently now he'll get himself back to sleep without fully waking and if he's not ill he'd usually sleep through now. I then go to bed and get up if either DC wakes during the night. Whatever time DC2 wakes after 5am is officially morning and DH gets up with him. Again, it gets better - default time is probably 6am. Unfortunately every cold/ear infection/tooth causes regression and it's closer to 5 for a week or so.
We've never used a dummy but if we had used one, I wouldn't take it off an 8m baby - that's got to be the worst time, really, just as they're going through such major developments and entering separation anxiety phase. Both mine had their worst sleep phases (bar illness!) at 8m and 13m. I'd wait a bit till communication and understanding are better (though I'd probably stop giving in the daytime by now, just to try to reduce reliance).
I wouldn't do cc either - again, lack of understanding. I leave DC2 to cry for a couple of minutes now on occasion, but a) he's in a bed and his door is ajar, he can get out and come and find me if he really wants and b) he needs to learn the world doesn't revolve around him and just sometimes his big sister may also need me at the same time!
Good luck.