Unfortunately your hope is about to be dashed.
The rights to the original set of railway series stories (and the locomotives depicted therein) is retained by the publisher of the original books (and their successor companies) which now means the lie totally with Egmont and not with the Awdry family. As can be seen from the date in your photo this deal was done a long time ago - although that book you photographed says 1954, Reverend Awdry had his first book published as early as 1945 when steam locomotives were a everyday sight on the UKs railways, the concept of railway preservation did not exist and nobody could foresee 'Thomas' turning into the massive brand it eventually did. As things stand Christopher Awdry cannot publish anything that is related to the original 'Railway series' unless the owners of the Publishing rights chose to let him, plus agreement would also be needed from Matel if said stories also include any of the characters they use in the TV series (this is why you have Brit Allcroft and HIT Entertainment being mentioned on the rights page along with Egmont).
Brit Allcroft went and bought the television (and movie rights) from Reverend Audry in the early 1980s, having encountered him and his stories while producing a documentary for the BBC about the Bluebell Railway (the first ex-mainline standard gauge railway to be preserved in the UK and a pioneer of the thriving UK Heritage Railway sector). Although she could see the potential in his stories, the fact it took her an awful long time to raise the finance to actually get the series made shows that nobody (probably not even the good reverend) expected the Thomas the Tank Engine & Friends series to be the hit it was - and that was reflected in the deal which gives total control of all aspects of the Thomas 'brand' to the TV rights holder and zero say to the Awdry family.
Therefore when it comes to licencing toys etc - then permission is needed from the owners of the Thomas the Tank Engine series for anything featured in the TV series (regardless of whether it appears in the books or not).
Now, as with many things that start small, while initially Brit Allcroft was fairly tolerant of 'approximations' (fir example the Hornby 00 gauge model of Thomas was created from an existing model of a E2 class locomotive and as such has a number of key visual differences to the TV character) the popularity of the brand caused things to be tightened up with grater fees to be paid and more attention to ensuring the 'look' of the TV series was maintained as much as possible.
The rot really set in when the company Brit Allcroft had set up to produce the Thomas series got swallowed up by HIT Entertainment in 2000. They massively hiked the fees charged and some measure of their mentality can be seen by their legal department sending a 'cease & desist' / "You must stop having an engine named Stepney or pay us a massive fee" letter to the very same Bluebell Railway that had inadvertently caused Brit Allcroft to encounter the Reverend Awdry and his Thomas books! (The Bluebell responded by pointing out that the locomotive in question was named 'Stepney' by the London Brighton & South Coast Railway back in 1882 and had been owned by the Bluebell since 1960 - so if anything it was HIT Entertainment who owed money.....).
As has been noted HIT Entertainment themselves ended up being taken over, etc and the Licence for Thomas the Tank Engine merchandise now solely rests with Matel. As to whether they let other toy companies produce Thomas merchandise - well the answer is it depends on the individual circumstances. For example Matel are not in the business of making 00 / HO gauge model railways so in these cases they are happy to maintain previously negotiated arrangements with Hornby / Bachmann (subject to enough money being paid to Matel of course - which is why Hornby, who are not in the best of financial health, have decided to drop the deal).
The upshot of all this means if you want an official Lego 'Thomas' based product then the only way they can do so is to buy the licence from Matel - who are quite likely to refuse if they already have a Lego style product amongst the brands Matel already own.
The Awdry family have absolutely no say whatsoever over the 'Thomas' brand however sad that fact may be.