It looks like MOST of your body needs are taken care of by [BODY:HUMANOID_2HEAD] [BODY:TAIL] [BODY:3FINGERS] [BODY:5TOES] and [BODY:1EYE] in the default body files.
1EYE has [CONTYPE:HEAD], which means attach it to every part that is of the head type - so you'd get one eye per head in this case.
You're going to need to add some new body files - either append into the existing body_default.txt or make a new file. I'm going to assume you're making a new file here (I prefer this method; keeps my stuff separate from the default files so I can update/troubleshoot easier). Let's say you create body_earwig.txt for these new body parts. The first lines of your file would be:body_earwig
[OBJECT:BODY]
Now, looking at your creature, we need to attach two mouths per head.[BODY:2MOUTHS]
[BP:MOUTH_U:upper mouth:STP][CONTYPE:HEAD][MOUTH][SMALL][EMBEDDED][APERTURE][CATEGORY:MOUTH]
[DEFAULT_RELSIZE:20]
[BP:MOUTH_L:lower mouth:STP][CONTYPE:HEAD][MOUTH][SMALL][EMBEDDED][APERTURE][CATEGORY:MOUTH]
[DEFAULT_RELSIZE:20]
Because it has CONTYPE:HEAD, it attaches an upper mouth and a lower mouth to each head. You'll end up with body parts called upper mouth, right head and lower mouth, left head for example.
As for teeth - sounds like you'd have a bunch of teeth all the same size. That's what [BODY:GENERIC_TEETH] is (30 teeth in that one). You can't specify shape of bodyparts, only size. Now, the generic teeth are all relsize 1, so I'd probably increase that for your creature. Unfortunately GENERIC_TEETH have CONTYPE:HEAD. We'd want them attached per mouth, not head. New body part![BODY:TEETH_PER_MOUTH]
[BP:TOOTH:tooth:teeth][CON_CAT:MOUTH][CATEGORY:TOOTH][NUMBER:30][SOCKET][SMALL]
[DEFAULT_RELSIZE:10]
Putting it all together - I'd suggest [BODY:HUMANOID_2HEAD:TAIL:2MOUTHS:TEETH_PER_MOUTH:1EYE:3FINGERS:5TOES:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:SKULL:RIBCAGE]. Bolded ones are ones you'd have modded in.
I don't have the FACIAL_FEATURES body tag in there. If you want them (cheeks/lips/eyelids) you'll need to make a new body part with some adjustments - for lips and cheeks, probably change [CONTYPE:HEAD] to [CON_CAT:MOUTH] and remove one of the eyelids since you only have one eye per head.