The copyright date is not much of a guide to value, I'm afraid, as that appears in every copy published to this day; it's far more important to know when they were published.
Condition is also super-important: Tintin books have become collectable and gained a monetary value, but they were also printed in large numbers, so the better kept books sell for better prices.
The Francophone collectors market is far more mature than the English-language one, and it has managed to identify the minute variation in impressions, editions and quantities of books published, which means that a standardized system of grading and identification has developed - an area in which I am not an expert.
However, if you are working in the knowledge that these are early books (because you know who bought them and when) in good condition, you might want to approach one of the large auction houses which stage sales of Hergé, Tintin and comics-related items throughout the year; they have expert evaluators, who could accurately gauge the rarity, condition and worth of these albums.
There is a sale coming up in Paris at Artcurial
; the PDF catalogue is here
, containing photos of many books and the estimates of sales prices, which could at least be indicative to you. However, bear in mind that these are just estimates, and the books pictured may not be the exact version you have.