I would install a positive air vent unit .
That way you aren’t relying on Opening windows and the air outside to be enough To ventilate. They are spot on when it comes to mould and condensation

I would always start with putting in trickle vents in the window openers of all windows first, as this is a cheaper option as this normally sorts the problem. But if it persists then fit a positive air input fan. You should also follow these rules which will cut down of moisture in the home.

Reduce the potential for condensation by producing less water.
Always cook with pan lids on and the heat turned down once the water has boiled.
只使用最少的水做饭vegetables.
When filling the bath, run the cold water first, then add the hot water, it will reduce the steam which leads to condensation by up to 90%.
Never dry the laundry on radiators.
Dry washing outdoors if possible, or put it into the bathroom with the door closed and the window open or the extractor fan on.
Extractor fans should be automatically humidistat controlled, not solely activated by the light switch.
If you use the tumble drier, make sure it is vented to the outside (DIY kits are available for this) unless the tumble drier is of the new condensing type.
Don’t use your cooker to heat the kitchen as it produces moisture when burning gas (you will notice the window is misting up)
Never use bottled gas heaters (Calor etc) as they produce eight pints of moisture for an average sized gas bottle.
Ventilate to remove moisture.
You can ventilate your home without making drafts. Some ventilation is needed to get rid of the moisture being produced at the time, including that from people breathing.
Use passive vapour vents if no trickle vents are fitted to the windows.
Kitchens and bathrooms require more ventilation due to cooking, washing, bathing and drying creating high levels of moisture which means opening windows.
Ideally these rooms should be fitted with humidistat controlled extractor fans (these work automatically when humid air is detected).
Close the bathroom and kitchen doors when these rooms are in use, even if the kitchen or bathroom has extractor fans. This restricts the moisture reaching other the rooms, especially bedrooms which are often colder and more vulnerable to condensation.
Allow space for the air to circulate in and around your furniture.
Open the doors to ventilate the cupboards and wardrobes.
Where possible, position wardrobes and furniture against internal walls i.e. walls that have a room on both sides rather than an external wall.
To reduce the risk of mildew on clothes and other stored items, allow air to circulate round them by removing false wardrobe backs or drilling breather holes in them.
Never overfill wardrobes and cupboards as it restricts air circulation.
Keep your house heated to between 16˚C and 18˚C all year round this will keep the walls of the property at a constant temperature which will help stop cold spots on the walls.

Air vent would help and so as the dehumidifers. Depends on the age of the house and type of construction though..

Have a look online for a product called a PIV (positive input ventilation). You can have a loft mounted units or wall mounted if the loft space is too small. This will help combat condensation issues, we would also recommend a good extractor fan to the bathroom