Hi! I have to make a cake to feed 300 ppl for our Family Reunion. I was thinking taking 2 16 inch square cakes and laying them side by side for the cake. Does that sound like something that can be done? 

Yes, I've done similar:)  Just be sure any doorways you have to pass through are big/wide enough for the board you have to use for a cake that big.  Your board must be no less than 18"x32"  I suggest using a wood board as that is going to be one heavy cake.  Two16" sqs  4" high will not be  enough servings. ..if I remember the serving #s right ... that falls just short of 300...you might want to add something like a 10" or 12" cake along with/on top of those.  

Thanks for your response!! Yes I will have a 10 round on top in the corner area with a tree on top. Any tips on how to frost it without it separating??

Ice the large one and the 10" seperately then put the 10"er on top.  Of course, it is on a cake board and probably should have 3-5 straws for dowel support in your 16"ers just to be safe :)    Are you using b'cream or fondant?  It would be safer to have the whole thing completed at least the night before transporting - espeically if it is b'cream.  Also, it would help if it is well chilled. 

I will be using buttercream.

@kakeladi ‍ should i cut the ends of the 16"ers that will be connected to each other. I'm wanting this cake to look like one big cake.

Having it finished the night before allows the b'cream to set/crust which helps hold the 10"er on.  If you are not used to transporting tiered caked you can use a 'center' dowel thru the 10" & 16" all the way into the base board to help hold it also.  Just don't rely on that...poor driving, accidents, potholes etc can still be a major problem :)