When my mother in law first came to live with us, and she got especially
argumentative and restless in the evenings, a couple of Tylenol PM tablets
used to really help.

Then later I cut it down to one, and still later I didn't give them to her
at all, because she would go to bed with no hassle and stay there without
any problems.   This was due to the progression of her illness though.

They both need to designate a Durable Power of Attorney for their
medical decisions NOW so that someone else can make those
decisions for them when they can't.  Especially at their age,
everything can change in an instant when one of them has a
stroke, an accident, or some kind of medical crisis.

No matter how reluctant they are to discuss these matters and
their wishes for terminal care, YOU MUST TALK ABOUT IT NOW and
get the paperwork out of the way.  You do NOT want to be stuck in
a situation where they are both either incompetent or to ill to
make decisions.

Please convince them that it's in their interest as well as those
of their children that they do so now.

who is administering her meds?  if she has a memory impairment,
it's very possible that she may be alternatively not taking her
meds or overdosing, because she may either think that she's
already taken them when she hasn't, or that she hasn't when she
has.  erratic medication is one of the giveaway signs of
dementia, and someone overdosing on thyroid would probably be
agitated and have trouble sleeping.  if she's administering her
own meds your father should start doing it instead, being sure to
check it off on a written schedule.

the other think to remember is that she may be getting agitated
or argumentative because her reality is different than your
father's but he doesn't understand that.  agitation can often be
relieved by NOT attempting to correct the impaired person, but
simply acknowledging what they are saying.

argumentative, because she doesn't remember doing or not doing
things, or putting things in odd places, agitated because she no
longer has control of what she remembers.  wouldn't you be upset
if you couldn't remember what someone said to you 2 minutes ago,
or where you just put something you had in your hand a minutes
ago?

please get yourself a copy of "the 36 hour day" as i previously
suggested --- there is a lot of info in there about behavioral
problems and how to deal with them.  if you go to google groups
and google the archives of this newsgroup for "agitation" you
will find a lot of info about what the folks in the group have
tried.

for many, what worked was to have the loved one's doc prescribe
psych meds to deal with delusions or agitation, but one reason
you need a precise diagnosis of the type of dementia is that
various psych meds work differently depending on the type of
dementia.  many psych drugs aggravate rather than help agitation
in patients with frontal lobe dementias, for instance.