Lets examine the potential validity of both these rumors.
Current Barcelona goalkeeper Victor Valdés appears on his way out of the Catalan club after publicly stating he would not be signing a new contract. Pepe Reina came up through La Masia -- the Barcelona youth system -- and has European experience. On the flip side Reina would be at best a lateral move for Barca and in many ways a downgrade for my money.
Surely Barcelona could do better than Reina with all the resources available to them.
As for Marquinhos, the 18-year-old defender has been in-and-out of the AS Roma team due to injuries, as well as his young age. There have been been reports that Barcelona scouts have been in Italy looking at the Brazilian. Given the apparent lack of depth at the central defender position, bringing in a promising young player makes sense.
However, Barcelona needs someone who can contribute immediately in the defense in place of Carles Puyol. Marquinhos has a bright future and could certainly be useful for Barcelona next season, but he's yet to play a full season at the highest level. This would have to be a move in addition to bringing in a more proven defender.