The name "Knights of the Shield" is very Paladinny. Are they?
Nope. While their membership consists of many noblemen, their main interest is trade. To further their goal of making money, they take a vested interest in politics, and their members include at least two Dukes of Tethyr and even one of Amn's Council of Six. While many Knights are upstanding, lawful citizens, many others engage in some very questionable activities - including slander, price fixing, tax evasion, espionage, and smuggling.
The Knights, who are secretive enough themselves, also have an inner circle known as the Shield Council, which most "regular" members of the organization don't even know exists. The Council members are all either LE or NE, and while their primary objective is the same as the Knights' - the manipulation of trade and politics for the organization's collective benefit - their activites they sponsor are even more dubious: kidnapping, blackmail, conspiracies, assassination, etc. The Council has agents and spies in 70% of all governments in the Forgotten Realms, the major exception being Waterdeep.
Unknown to all but three of the Shield Council's seven members is that the Council itself answers to a high power - namely the Demon Lord Gargauth. Precisely what his long term objective in regards to the Knights hasn't yet been revealed.
Incidentally, the two Knights in BG1, Tuth and Kestor, are cannonical members. Both reside in Baldur's Gate, the former being an ex-adventurer who killed a dragon (while it slept) and claimed its' horde, and the latter being a major figure in the Merchants' League, owning an entire fleet of sailing ships. Tuth is actually a member of the Shield Council, but he is their scapegoat - if anything major should go wrong, the rest of the Council will attempt to place the blame on him.