5. Their trip was OK, but they would have enjoyed it more if the weather had been better.
В данном предложении использовано смешанный тип условного наклонения. Первая часть сложного предложения (they would have enjoyed it more) выражает условие в настоящем, а вторая часть (if the weather had been better) - нереальное условие в прошлом.
Ответ: they would have enjoyed, had been