If you're doing the crowdpleasing thing of raisins/sweeties in-between each layer and making sure everyone gets one then that's very tricky with 2 simultaneous parcels in the same ring, or even with two in different rings.
Am liking 'pass the teddy' idea too....saves on wrapping! Definitely do 2 (or 3) circles and do lucky dip or a sweet jar for each 'layer' and then one main prize. It can turn into a nightmare as kids wander off, get bored and 'forget' to pass it on etc so the less time they have to wait their turn the better! Good luck
We do pass the teddy/ sweetie bag/ etc at school for the Xmas party, much easier than trying to wrap a prize in 30 layers of paper! The parcel ends up too big for most of the children to pass anyway, even if you do two they get quite big.