new horses

That's  a tough one.   How long did you have the first two - they've obviously bonded.  And how long have the other two been in there?  And how big is your enclosure?
My herd of 4 includes 3 big dominant Standardbreds who were ALL alpha where they came from so they had to sort out who was the boss.  I tossed in a rescue filly who was 1-1/2 and they all went "awwww... she's MINE!"  so the alpha got the filly to be uncle to.  But when they are paired differently, the 2nd was uncle.  The 3rd is a playbaby so they spend a lot of time frisking. 
NOW my 2nd is blind and the 3rd gave him HECK until he realized ol' 2nd wasn't going to put up any argument about pecking order!  He's just happy to be left alone.  The filly stands with the blind horse.  She's probably over him now but she's nice to him so that's cool.
If they've been together for a while and no one's gotten killed or seriously injured it will probably settle down.  Mine have had so many teethmarks, scuffs, hoofprints...  That's really what horses do.  Herds are natural and I think they'll sort things out.  HOWEVER I've heard of horses killing other horses so I'm not saying pay no attention.  I just think, if the new gelding was serious about eliminating the other, there's be one less horse.
If you can load up the 2 geldings and haul them somewhere - anywhere - maybe for a trip to the park or someplace you could unload them, tie them to the trailer, groom them, walk them around.  Picnic....  load them up and take them home...
Those kinds of things help bond them.  Even just hauling them around for an hour! 
We have some great trainers here - I'm not one of them.  This is just my 2 cents.  I hope it settles down on the farm! []

We just introduced 2 new horses to a herd of 4, now we have 6.

The new ones just came home, for the 1st time, from a stay of 2 months at school. The trip to school was the first time these two met. It was not pretty. A Arabian mare was picked up 1st. Then we got our paint gelding. Everytime he would get in the trailer she would start kicking. Needless to say, he refused to get ion the trail. So, we took her off, and then managed to get him on. We then loaded her but had to put an empty space between them. All in all, it took 3 hours to load them and they broke 3 trailer ties. While at school, they had no interaction with each other other than a couple times in passing, in which he remained terrified of her. On the last day of school, we loaded him 1st, then her, this time did not separate them. No issues this time.

Once home, they stayed in the barn for a week in stalls next to each other. They were turned out a couple times without the other 4 in the pasture. This was there first big test. The trailer ride and staying next to each other worked. When they got in the pasture, they were best buddies. During the week, we also added one of the other horses to the mix.

When we finally put them out with ALL the other horses, 2 days ago, they pretty much were 4 against 2. However, there were no serious issues. Yesterday, they seemed to be sorting things out and hanging closer together.

If you have opportunities to get horses to reside next to each other in a barn, that will help. Mix it up some. If you have a meany, take him out and let all the others in. Of course, it all depends on what facilities you have available.

When we were boarding one of our horses got pushed through a wooden fence (through the wooden post) and got stabbed. The broken post went up between his legs and came out his chest. Luckily, no organs were hit and he was fine, though out of commission for a few months.

Below is a short YouTube video I did when we first put all six in the pasture.
Eros & Starr Join The Herd

GOOD LUCK!

Oh wow face that was too cool!  She's a fiesty mare, isn't she? And he's definately her herd!  He was hiding behind her every chance he got!  She'd be a great alpha!  Love the slo mo! []
The other 4 look reasonably peaceful.  Great looking horses!!