First off I want to say if You are in a guild that is not running Naxx or only clearing 3-4 bosses, you should absolutely be clearing more with any form of even moderate dps'ers.
There really is no excuse not to have all of spider wing on farm, all of plague wing, and 1st two bosses on military ward. These are all relatively simple fights that tke minimal time to learn, and ensure you are downing maximum bosses.
The one possible exception here is loetheb. If you don't have the dps to ensure a good kill, then just do the other bosses and come back to him last.
In any event, we 2 pally healed this instance this week in my guild with mostly first time members(this was our guilds "c" team) and our top dps was 1600 on most fights. This is abysmal dps compared to our "a" team, and yet we downed all the way to gluth in constuction quarter, and every boss in the other quarters.
With paladins using beacon of light properly by talking about what tank gets the bol, there is no excuse for paladins to be not keeping the raid up anymore.
Also, I strongly encourage naxx to be done with 2 healers. The extra dps is nice. However if your healers are around the 1500 spellpower number vice 1800+, then bringing three healers is fine, but the fights will tend to drag on.
Just remember that every ifght has a trick for most healers, and if you learn what that trick is the fight becomes much simpler.
On Maxxeana, use holy shock after the web spray and the fight becomes trivial.
On Heigan you should be cleansing debuffs asap while other healer(assuming they have no cleanse) heals. if you both have cleanses, then what we do is we dedicate 1 healer to cleanse and the other helps with 1 cleanse right when it happens, this is enough to get you back into the fight 1.5 seconds quicker, with onyl minimal loss of healing for your raid, which is fine since this is not a hard fight to heal.
Just really learn what to do on each ifghts. I strongly recomend all healers take the time to read the fights and boss abilities on www.bosskillers.com and www.wowwiki.com and others.
I know i haven't said much concrete in the way of how to do things, because every paladin plays differently. For example, on patchwerk, we had 2 holy paladins helaing, and when I looked at our combat parse later, I saw that both of us did almost exactly the same amount of healing literally within 7k of each other. I spammed fol the enttire fight and he used holy light primarily, so it would be wrong of me to say, do this method or that method.
Also, make sure your raid understands every boss downing is important as it helps your guild thta much more for the next time.
And on a closing note. Spider wing and Plague wing are actually easier, imo on naxx 25 than on 10 man, so if you aren't dedicating at least 1 night to naxx 25 you are shooting yourself in the foot as well.
Gl all.