It's not uncommon to see multiple plantings of palms, all it tends to do is make the trunks curve out from one another as they grow. Runts in the group however can sometimes be starved by the stronger growing ones and wither away. I have a couple of clumps of Sabal minor around head height which look quite good. So I think thinning them out would be more of a personal choice rather than what the plants need.

I'd rather them grow in a clump, I think it would look more natural since I'm letting my yard get semi-wooded. Maybe the trunks will grow apart to prevent any rubbing issues in the wind.