With this two hunters have to take turn on casting mark,

NOTE ","

/castsequence Hunter's Mark, --hunter a
/castsequence ,Hunter's Mark --hunter b

also add /petautocasttoggle Growl --make sure one of pets have it turned off, so this will make pets take turns on tanking.

rest leave as it was, and do keep an eye on pets health and heal it as needed, dont let it die in a first place.