It is reasonably questionable if any of your family members will ever understand why Catholics pray the rosary. Part of the problem is that in reaction to some Catholics intense devotion to Mary and the rosary in the past, Protestants who were not “high church” saw it as idolatry.
If you want information which you could condense to some understandable but Scripture-based, then you might want to buy the book by Brant Pitre Jesus and the Jewish Roots of Mary: Unveiling the Mother of the Messiah.. It is about $16 on Amazon; or you might find it available for sale in a rack at a local parish (they may be able to obtain a special edition at a lower price).
In fact, I would recommend it for you even if you don’t intend to do the work to bring it down in bite-size chunks for them. And there are absolutely no guarantees they will even actively listen.
I have found many wonderful Protestant brothers and sisters, people who are very faith filled and love the Lord. And many of them are extremely wary (some, to put it politely) of Catholics and anything to do with the Catholic Church.
You don’t say your age; if you are still living in the family home you need to not ony be polite, but refrain from pushing issues they don’t want to hear. And that may include taking some “abuse” concerning Catholic issues. Charity would indicate a meek response.
On the other had, without going into a nuclear meltdown, if you are taking heat and not living at home, you may be justified in making it clear you are not going to pick at them about their faith background and understanding, and you expect the same respect to yours which you give to theirs.
No matter the result, Brant is awesome and I highly recommend any of his books.