Innerspace is the platform, but IS Boxer is the boxing software which runs on the platform.

IS Boxer is free, but requires an innerspace subscription, which runs $10 per 3 months or $36 per year. If you mention someone as your referral, you both get extra time. I believe you get 15 days on the 3 month and 30 days on the year, if you mention a referral.

With IS:Boxer, you'd make a Keymap.
Keymaps have a hotkey to activate.
And can be configured with unlimited steps.
A step is a unique action which occurs on a keypress.
Most keymaps have one step (always do the same thing).
Toggles generally have two steps (one thing on press 1, the reverse on press 2).

You'd probably go with 2 steps per paladin in the group.
So 8 steps for 4 pallies, if you are running 4x Pally + 1x DK.
The first two steps have Pally A as the target.
The next two steps have Pally B as the target.
Etc..

You can go with "send a keybind" to warcraft.
And have the DS and DS keys, on two separate keys in wow.
Which lets you run the toons as individuals, and still have all your keys.
But you can also generate your macros inside of IS Boxer, in which case you have 1024 characters per macro, but then it won't work 1-boxed without ISB.

Basically set each even step, to not advance to the next step until "x" seconds have passed.
Something like say.. 5 seconds.
That will allow you to spam it frantically for a few seconds, to have the spells go off.
But should not impact the next desired press of the next version.