1) So we have this h1adith in the book of Kafi, from Imam al-Sadeq (a), that says:
أبي عبدالله ( عليه السلام ) ، قال : ألبان البقر دواء ، وسمونها شفاء ، ولحومها داء .
“The milk of cows is medicine, their fat is healing, and their meat is a disease.”
This means that the milk and fat are beneficial whereas their meat is harmful.
Now it’s ok to eat beef occasionally. One should avoid eating it everyday or on a regular basis. Based on our hadeeths, lamb is better than beef.
2) Regarding the argument that the Qur’an says it’s halal, yes of course we agree it’s halal. The hadith does not reject this. The hadith just indicates it’s not recommended to regularly eat it. So it’s not contradicting the Qur’an for us to reject it. Cows also have other benefits like milk and fat too, so we keep that in mind.
Here’s an analogy: the Qur’an says that sea hunting (like fishing) is permissible. Does this mean it’s recommended to eat every sea animal? Of course not. This is a general verse which does not go into specifics.
In any case, it’s ok to eat beef. I don’t recommend you let this become an issue with your family. In the end it’s perfectly halal and permissible. Yes, personally try to eat it less (try not to eat it every day) and instead if you want to eat meat eat more lamb as it’s recommended.