>Therefore i formulated: あなたが私のことをあなたの息子だと思うのが嬉しいDoes this make sense? Yes, it is grammatically, syntactically correct and makes sense but it does not sound heart-warming. Your sentence sounds like "Gaijin-like" or "European-language-translation-like" but it is no problem because you actually are. And if I put a "language-soy-sauce" in your "translation-like" sentence to make it sound like heart-warming Japanese, like ： あなた　→　みなさん　or お二人（because they are two) あなたの　→　自分の 思う　→　思ってくれる, that would be: みなさんが私のことを自分の息子だと思ってくれて、とても嬉しい お二人が私のことを自分の息子だと思ってくれて、とても嬉しい

Just to let you know, other than "くれる", you also use "もらう" often in order to express thanks for someone. If you could use these two words properly depending on the context, you might sound more like a native spearker of Japanese. ／彼に空港まで送って ｢もらって｣ 本当に助かった。

It is not easy to explain the nuance of "くれる" in English, though I would use an adverb "kindly" as below. ／i.e. I was really lucky that he kindly pick me up and took me to the airport. 実に幸運なことに、彼は私を (親切にも) 車に乗せて空港まで送って ｢くれた｣ 。

Please worry about yourself more than me. ／ You can say "あなたは私のことよりもっとあなた (or あなた自身) のことを心配してください", though "あなたは私のことよりもっと ｢自分｣ のことを心配してください" is more common.

I know you would like to say "I am glad you two think of me as your own son". ／あなたが私のことをあなたの〔あなたの or 自分の. I know it is quite natural in English to repeat "you (or your)" here, though you more often use a reflexive pronoun "自分" in Japanese.〕息子だと思う〔思う or 思ってくれる. You often use "くれる" in Japanese when you would like to express your thanks for someone. Actually, SO often that some people might feel it a bit impolite if you didn't use it as in your original sentence.〕のが嬉しい。／