I'll answer from the perspective of a 5 x L63 Lock team.

1. Demon Summoning... no way you're going to have enough buttons to have them on a per-warlock basis, unless you go mad with something like Trinity bars.
If I lose 1 or 2 demons during combat then I'll just move the mouse to that client and manually click the button to summon.
If I lose 3+ demons then I will tend to just use KeyClone to summon on all 5 and then try and remember to drain soul on the next kill to make up for it
If I'm panicking mid-boss fight and am down 3+ demons then I'll use everyone's Fel Domination and get a fresh set of demons out pronto.

2. Life Tap... more difficult for me to answer as with a 5xWarlock team and no healer I actually tend not to use it much for the inherent danger of low-life and getting aggro.
However, again, I just have one button assigned and all Warlocks life-tap if need be but not that often, to be honest.
I took 3 of the girls out with a pally and a priest the other night and it was lovely to have dedicated healing for massive hellfire use and lifetap

3. I use the Pitbull addon to see who each Warlock and each Pet has targetted. I then have macros for all to take my target and 4 buttons set aside for the clones to individually take my current target.
That way, on a larger pull, I can assign 5 targets and send the pets in against those 5 targets, then re-assign the warlocks to the kill targets in turn.
I find this works really well for me.
I have another button, on RR, to send the next pet against my current target, should one of us get aggro and need a pet to relieve them of it.
Pitbull also has the huge benefit of being able to easily see each Warlock's life/mana and each demon's life/mana.
The default interface is way too small to see any of that detail.

Here's my Warlocks with Pitbull... and, yes, I do use raid icons a lot
The Felguards are targetting one tree, orange symbol, whilst the locks are all targetting the second tree, skull.
A simple example but it demonstrates how Pitbull makes it much easier to monitor all Warlocks and Demons and their targets.



You don't mention your spec... have you improved your Voidy and bought the training books for torment/suffering etc?