I have about 20 friends coming over this weekend and we plan to eat only sausages. I have bought a variety of sausages and this will be my first time BBQ-ing. I have bought several packs that are marked "fully cooked" so I am assuming I can toss them on the BBQ for ten minutes before they are ready to eat. I have bought 3 packs that did not have the word "fully cooked" or "pre cooked". Should I be poaching them in water before BBQ-ing? In addition, there is one pack that came frozen. Should I also poach the frozen pack prior to BBQ-ing?
Those are what you would refer to as "Hot Dogs" in American parlance.
They can be heated by any means you deem suitable, including boiling, microwaving, baking, frying etc. They do however need to be heated fully before they are ready to consume.
They commonly contain a lot of sugars, so burn readily on a grill if the grill is too hot or the hot dogs are not rotated frequently enough.
They do not need to be boiled before grilling in any form, but it can make it easier to preheat them before cooking on the grill so that you can achieve an even browning or the much desired "grill marks" without burning before thorough heating is achieved.
Edited to add: it has been pointed out to me that the package at the bottom of the post showing Marc Angelo chicken sausages are uncooked. This means they are not hot dogs like I largely described. Definitely do not boil these. Give them a light oil coat and put on low to medium heat on the grill for about 30 min turning regularly to ensure they don't burn.
It's not necessary to poach sausage before BBQ-ing. If you afraid you might get not cooked in center and burned outside skin due to charcoal fire is hard to control or first do BBQ-ing as you mentioned, then poaching before BBQ-ing might be a good choice. At least you won't get any inedible foods.
You could use toothpick to poke some holes or use knife to cut some lines onto the sausages before BBQ-ing, making the center more likely to get cooked. And turn the sausage frequently on the grill meshes, shall you will get nice cooked and yummy sausages :D
Recruit a friend.
Of 20, presumably Canadians, someone must have a clue. Since this is explicitly a sausage party I am going to assume it is a he. You know who he is or maybe you will find out when the party starts. Have a couple of expensive beers set aside for that person. He will hopefully be proud to know that his expertise is recognized. He will teach you how to grill for this occasion.