I would take a side off the cot bed, which would make a great way to transition.

I think you give yourself already pretty much the answer. Dare to trust yourself and follow your own intuition; mum does know best !

Rio off the bandaid so to speak. You might have a couple of restless nights but they will quickly get used to it if there is no other option. Maybe get them to help you pick out new bedding or a new cushion for there new bed and spend a few hours playing in the room with the new setup. Kids love balloons (generally) so maybe have some fun with a balloon in there in the afternoon to take some worry out of it.

Thank you all for all of your answers. I have thought about moving them to a mattress on the floor – either their cot mattress or a bed mattress. But i don’t think this would work. They have seen their older sisters bed and they love it – it’s just trying to convince them that a bed of their own is a great idea! They play in their sisters bed, play ‘sleeping’ in it but won’t have a bar of themselves being in a bed. Having a ‘sleepover’ in their sisters room would be a nightmare as she is still a bad sleeper. She will wake at anything and takes ages to go off to sleep and is distracted so easily! If she had 2 other little people she’d be awake all night and try to keep them awake!!!
My twins generally chat to each other for 5-10 mins then crash out and go to sleep. All 3 together would end up in one or all 3 waking the others and keeping them up. We’ve done this on holiday and no one got much sleep!
When I think about it, I think it’s more about them seeing their cots as their bed. When I get them big beds, they will be the same make as their sisters so they know what it will look like and feel like. On holidays they’ve slept in portacots but didn’t sleep well. Now they are too big and portacots aren’t safe when we’re away. Another reason for getting them into single beds.
I am inclined to leave them as they are as a couple of people have suggested. It’s just a matter of space- taking their cots out and having single beds will allow us more room in their bedrooms. Thank you for all of your responses and suggestions. I really appreciate them all. Happy if anyone has any other suggestions? My reason for wanting moving them is because they are almost toilet trained but at nighttime still wear nappy pants. But often one of the 2 will wake up in the middle of the night and ask for the toilet. If they were out of cots they could take themselves to the toilet. In which case I would get a baby gate to make sure they could only access their room and the bathroom. If it was just one child I could probably handle getting up at night for toilet requests – but between the 2 of them it’s a bit much! I’ve only just gone back to almost full night sleep after their baby years.
I’m not sure what to do? More encouraging to go to ‘big’ beds, or just get the big beds and get rid of their cots or leave them until they want a big bed?? Yes it is a parenting frustration. Any other suggestions?

Oh dear, this is the fun bit for a lot of parents. I would suggest you keep doing what you’re doing. Maybe have a ‘sleepover’ in their sisters room, at least they’re out of their cots, and if they have enough fun it might be a step in the right direction

If they still fit in their cot, I would let them stay in it until they are ready to move.
My daughter decided at 3 that she was ready for a big girls bed and we haven’t looked back.
You could also just show them some beds at a shop one day

We started by using the cot mattress on the floor for day naps, then took our child shopping to choose out their own big bed. We then used the single mattress for the day naps and eventually put this onto the bed frame with the cot mattress on the floor incase they fell out. We didnt bother with side rails at all with either of our children.
We invested in a baby gate to stop them from coming out of their rooms all the time.