Hi Wendy,
I wish I could answer in one sentence but it would be impossible. At least it looks like they will be (or should be) around the same level. That�s always a godsend when teaching languages to groups.
There are some assessment tests on this site, but you�ll also find plenty of internet. Depending on their level you could follow up with something to "break the ice" / form the group, even if they know each other, it�s all good fun.
Here are two of my favourites:
1. First of all ask each student to introduce him/herself to the class. Then select pairs around the room (not sitting next to each other - opposite if possible). Next hand out a sheet of paper to each student and ask them the draw just the head/face of their "partner" adding specific items which will help recognize the person - glasses, hair, etc. (they MUST NOT add the name). They don�t have to be artists that�s the best part of it. When they have finished, collect them and redistribute them around the class being careful not to give them to the same students. Each student must say who he/she thinks it is and what they know about him/her from the introductions they heard earlier.
2. Get a volunteer to draw a quick outline of the country on the board. This one works much better if they all come from the same country, but can be adapted in multi-national classes. Each student comes up to the board and puts a cross where he/she was born. They then tell the class something about themselves, their families and the town they were born in. Of course this may be limited depending on their English level, but it doesn�t matter. I even added myself and started the exercise.
Prepare a couple of revision exercises to get you over the first few lessons. They WILL need them!
You�ve come to the right place here, you�ll find plenty of good worksheets to use. Good luck !
Janet