i used to use AHK to run my tank and healer at the same time and levelled up through LFD (I'm not sure if I would attempt to do this in heroics with that setup, but for levelling its fine).

for your healer you need a basic spam macro. If you are running a tank/dps and you spam say "2" for your tanking/dpsing macro rotation, for "2" on your healer you want a macro that runs a cooldown limited healing rotation that your healer can keep up without going oom. i happened to do this with a resto druid, so I'm most familiar with these kind of macros. here is a resto druid example:

/focus TANKNAME (change the name at the start of each instance)
/castsequence [@focus] reset=combat rejuvenation, nourish, swiftmend, rejuvenation

this macro is limited by swiftmend (15 second cd), so it will cast these four spells every 15 seconds.

Now in addition to this you also want the ability to heal the individuals in the party without switching windows, so I used to use, on numpads 1-5 a simple macro like this

/castsequence [@player] reset=5 rejuvenation, regrowth, nourish
/castsequence [@party1] reset=5 rejuvenation, regrowth, nourish
/castsequence [@party2] reset=5 rejuvenation, regrowth, nourish
/castsequence [@party3] reset=5 rejuvenation, regrowth, nourish
/castsequence [@party4] reset=5 rejuvenation, regrowth, nourish

Once you have wild growth (or another party heal), you'll also want to keybind that. You can incorporate it into your spam macro such as

/focus TANKNAME
/castsequence [@focus] reset=combat rejuvenation, nourish, swiftmend, nourish, nourish, rejuvenation, swiftmend, wild growth

or just keybind it by itself.

honestly to level this will get you there, especially if you have heirlooms on your tank and/or healer, and you don't have to be perfect while levelling