Hi, it's so hard to say the cause of these by just looking at pictures personally if you are looking to purchase this house I would get a professional in to assess this.
Not really an expert on this exact field of paint i would probably say spray would be best but I get all my paint from https://promain.co.uk and swear by the products they supply.
Keep furniture to a minimum and make sure the furniture is relevant to the room. Paint the bedroom using a neutral colour Also hand mirrors the effect they have are unbelievable.
It is ideal to paint in warmer weather, although if you could somehow make an artificial source of heat this would suffice failing that you won't always see the best ever results.
I would definitely contact Dulux, just be careful they don't try to give you the run around and shirk the blame on someone else like as previously stated how the paint is applied.
Personally I would recommend the Masonry paint as you mentioned it gives you the weather protection although both choices have their pro's and con's I would choose masonry.
