That's all easily sortable 
They are decent naps, although 6m is very early yo have dropped the 3rd nap. The only thing I would suggest to improve your routine on 2-nap days (which may improve your night sleep) is the 234 awake windows of 2-nap days. So aim for each awake window yo be longer than the last. 2h for the first awake window, then 3h then 4h until bedtime. I notice your awake window between the two naps is 2h. This may either mean your 1st nap needs to be earlier or your 2nd nap later. Getting daytime naps right helps avoid over tiredness over night.
Onto the dummy. I can see straight away your fundamental error:
But I am worried about it falling out through the night...
The dummy is meant to fall out. If you are expecting the dummy to stay in baby's mouth all night and so are considering it "Not working" if it's not, then you have absolutely the wrong idea of dummy use.
The purpose of a dummy is to assist baby to calm themself from being awake, into the light sleep phase.
From the light sleep phase sucking stops (Dummy served it's purpose) and baby fairly quickly goes from light sleep to deep sleep. Once in a deep sleep then all of the muscles in the body relax, that includes mouth and jaw muscles - the muscles holding the dummy.
So the dummy is meant to drop out. That is the "tell" that baby is now in a deep sleep. It should take about 10 mins in an ideal world - that's the only length of time dummy is in baby's mouth.
So baby gets into a deep sleep, mouth slackens, dummy drops. Now what? Well on from here you have to tackle whatever is the reason for baby waking frequently. It's not the dummy. Dummy has no relevance on baby waking up.
There are a million reasons that could be causing baby waking. Not going to sleep in the cot is a common reason from 4 months onwards. Or the need to comfort feed or hunger, especially around weaning. Over tiredness is another very usual one, or poor daytime routine.
All the dummy does is make going back to sleep easier and quicker (with fewer tears). With nothing causing baby to wake frequently, baby's sleep is cycles of deep sleep > light sleep > deep sleep > light sleep > deep sleep > light sleep... and so on. Usually the periods of deep sleep are longer at the start of the night and get shorter.
You'll note that high quality sleep does not involve > deep sleep > light sleep > awake. There is no waking in good quality sleep. Since the only purpose of dummy is awake > light sleep, it has no effect on waking up. It has no effect on staying asleep. It only improves going to sleep.
So rather than focusing on the dummy. You need to dismiss your dummy shaped red herring and start working out what's causing baby yo wake up.
One thing I didn't mention earlier is developmental. Some babies wake up simply because they are not developmentally ready for long chunks of sleep.
I don't know if any if this will help you? I hope it does. I know you have a bee in your bonnet that dummy is the reason for your baby's difficult sleep. I respectfully entirely 100% disagree with this.