I introduced 2 sows (mother and daughter) with a trio (neutered boar and two wives). I think half my problem was the fact that unlike a pairing you only have to watch the two pigs - i had to have eyes everywhere with 5 pigs to watch!
Looking back i also think i was a tad too panicky as i kept separating at the first sign of anything iffy - they say with sows acceptance happens much quicker than with boars and that you'll know within the first 30mins whether they will get along.
I eventually (after about 3months of failed attempts) bathed all 5 and left them in the bonding pen for about 9hrs before moving them to their permanent home - i dont think i moved for the whole 9hrs, in fact i dont actually remember having breakfast/dinner or tea.
My 1 sow was very dominant and she wasn't afraid to tell the others and this is why the dominance period lasted for days as opposed to hours - she really pushed the 'under' sows and for 2wks one of my sows (who is shy by nature anyway) ran away every time my top sow came anywhere within eye shot - she would scream in protest - it was horrid to hear/watch, but obviously it was a process that needed to be done in order for them to fully bond.
Looking back my situation was pretty easy in the fact that all other sows allowed my top sow to be just that - they didn't fight for dominance, she told them how it was and they all fell in line - i dread to think if one of my other sows had ideas of being top sow!
If it were me - i would set up a neutral area (without any hideys - just a big pile of hay/veg) and put them all together and see how they get on - you may be pleasantly surprised....
Have a dust pan handy to put between any pigs that look like things could get heated - this helps to quickly disperse any escalating behaviour. a towel is handy to have also in case you do need to break up any aggressive behaviour...
Good luck
