Thanks for the question.
Don't worry about being stuck or confused when explaining shrines that honor the saints of the Church. The punchiest answer I've heard was given by St. Augustine:
When God rewards us for our labors, he is only crowning his work in us.
So Shrines obviously could be places of worship, but they only honor the saint; they don't worship the saint.
I dealt with a similar question on Mary that you may be interested in:
In Catholic Christianity, worship is given to God alone and as Mary Ann alluded to: the Trinity is Father, Son and Holy Spirit. Jesus, who is Incarnated God, is consubstantial, or "of one substance" with God, the Father, so when we worship Jesus at Sunday Mass, we do worship the Father.
Displaying the crucifix is not idolatry. Canon Law requires that every Catholic parish has a crucifix.
Because it's the ultimate symbol of our Redemption: Jesus' saving Death on the Cross. The blessed crucifix, itself, is just a piece of wood or metal, but what it depicts is important to all Christians; we don't worship a crucifix, we worship Jesus, Our Lord.
Whether your brother is a Protestant or a poorly catechized Catholic, encourage him to consider buying a cheap copy of the Catechism of the Catholic Church to learn everything we believe as Catholics . . . plus with the advent of new technology there are now more and cheaper ways to read the Catechism.
Hope this helps,