For the past year, we've been considering the adoption of a "sibling group", exploring the idea in-depth.  

We will seek counsel from our clergy soon, but I'd like to solicit the wisdom of the forum regarding Catholic tradition on this issue?

Provided that you have sufficient maturity and means to afford them a stable home and family, that you intend to raise the adopted children in the Catholic faith, and that you will provide them with the same degree of love and affection of which you would afford your natural children, I cannot fathom how it could be other than a wonderful act of charity on your part.  In that regard, you would follow the example of St Joseph, patron of the Church, who loved and raised Our Lord as his own.