Yes, so long as there are no 2-4-1s involved it's actually quite straightforward. All that needs to happen is that the existing PNR is split, which is a relatively easy to do on Pegasus, just a few keystrokes. However if you know it's a risk I would be tempted to book it separately just to save hassle, though I guess there are some free seat allocations at stake here. Since you are Gold you have the TCP route open to you there anyway, which allows you to call up and keep your party together if you are travelling in the same cabin.