I believe we read clearly the rules when it comes stacking modifiers from talents and various sources, but still to check with the community: We looked at "Shield Fighter" and "Sword Fighter" talents at the end of the session when the XP was being distributed by my players. Both talents give you +1 PARRY and the condition is to have a shield and fight with sword respectively.
There are no limitations on the source and amount of modifiers to a roll (talent or environmental), therefore the PARRY bonuses from "Shield Fighter" and "Sword Fighter" will stack giving a character +2 modifier to the PARRY action. Same approach with other talents.