Is it possible to fit aquapanels

I would not do it! You should fit so called aquapanels (cement fibre boards) on to a dry, levelled wall. You don't want to trap moisture underneath it and you don't want them to fall off the wall with tiles that has become loose or just 'popped' (adhesive failed, those panels are heavy + the weight of tiles on top of them). Anyone who says it's ok to tile over tiles or put waterproofing over tiles should be avoided and kept at a barge pole distance. Do yourself a favour and have a proper bathroom refurbishment done by a specialist that will strip it to bare walls, level the walls and floor and apply proper waterproofing where needed. If you don't want to use aquapanels, you can go for waterproofing matts or fibreglass (this one smells strongly when applied). They all deliver same effect, create a water tight membrane. Personally, I prefer to use the original James Hardie panels, as I've seen one being kept in water for over two years without any effect on the panel itself. Membrane is also great, it will work out cheaper than panels and comes with a 10 year guarantee from most manufacturers. Fibreglass is very strong and is mostly used on roofs, so a very good option too. It is very commonly used in wetrooms. If you suffer from mould in your bathroom it simply means you do not have sufficient ventilation in place. Does your extractor fan have a timer? If so, adjust it to work for longer and if it doesn't fit one that has a timer and set it for at least 5 minutes. Shall this not be enough you can increase it further to 10 or 15.