Hmm.. it seem that selection of the route can only reduce to a
limited extent on how tough the climb would be. Generally,
first-timers who have never been physically active before, may face
an uphill task of climbing that mountain. Go light in my
opinion.
You better start to preparing for the upcoming trip to fully enjoy
the scenic, if not, you will regret that you even to sign up for
it! 
Oh yes. I suddenly remembered that it is possible, perhape you guys
can check with the guide whether your group can ascend from
Timpohon gate and descend into Mesilau to enjoy the best of both
that nature habitats can offer.
A sidenote for this: Unless someone in your group has prior
knowledge on how to descend via Mesilau route, if not the price
better be negotiated first before set-off. Dont worry about the
descend for Timpohon, it is a tourist route.
