I have seen all sorts of combinations of support people at births, ranging from partners, friends, mothers, fathers, siblings and in-laws. Whatever you choose is appropriate and fine but just make sure you're going to be comfortable. The last thing you want or need while you're labouring is to feel like you're being 'watched'. Whoever you choose make sure they understand what you want from the as a 'support person' and perhaps set down some 'ground rules' (like FIL staying away from your girly bits). Good luck