My little brother is getting married soon. We have been thru some
tough times in the past few years and I want him to know that I love
him very much and I want to reconcile. He loves Latin and is one of
the only people I have ever known that can speak it. So, I want to
learn how to say:

We laugh together, we cry together.

In Latin to let him know that I am genuinely sorry for the trouble we
went thru. I know that will let him know I am serious about
reconciling with him. So anyone that can help, I would greatly
appreciate it.

Based on five years of middle- and high-school Latin, my recommendation is

"simul ridemus, simul lacrimus" (together we laugh, together we weep)

pronounced (likely) as:  SEE-mool RID-ay-MOOSE, SEE-mool LAK-ree-MOOSE
  - if you can semi-roll the Rs and spend a little longer on the 
     RID and LAK syllables, it will give it an Italianate air
  - note that no one *really* knows how Latin was classically pronounced

* lacrimo/lacrimare is probably the most appropriate translation of "cry" here
* rideo/ridere is the most common translation of "laugh"

If you'd like to check up on this or look for other variations, I find
the following Latin-English dictionary useful:

http://humanum.arts.cuhk.edu.hk/Lexis/Latin/

search strategy (for a dictionary): latin dictionary translation

Thanks! Much appreciated. Thanks for helping me out of this one.

My Latin is not the best, so I am not posting this as an official answer:

"Gaudemus et comploramus."

It should be noted that 'ridemus', while it does mean 'we laugh',
carries a connotation of mocking or sarcasm. It comes from the same
root word as 'ridicule' and 'derision'.

Like PF, I thought 'ridere' had more of a ridiculing connotation also
but I found this Latin story that runs the gamut of happiness,
ridicule, derision, and laughter and it does seem to fit.

"Vos Graeci autem deos fabulis irridetis. (You Greeks, however,
ridicule/deride the gods.) Pro veris deis scurras habetis." (Instead
of true gods, you all have clowns.) Tum Demaratus dicit: "Cur nos
vituperas, Marce, quod deos interdum fabulis irridemus? (Why do you
criticize us, Marcus, because we sometimes deride/laugh at the gods in
stories?) Sine dubio veri dei ira vacant, et certe bonis iocis gaudent
et rident." (Without doubt, true gods lack/are free of wrath/rage, and
certainly they are happy and laugh at good jokes.)"
http://www.wvup.edu/Academics/humanities/Oldaker/latin_stories.htm

Also from this page there are very similar-sounding words in
Esperanto,French, Italian, Occitan, Portuguese, Romanian, Sicilian,
and Spanish.
http://www.websters-online-dictionary.org/definition/english/la/laugh.html

Perhaps 'ridere' could use a qualifier to avoid misinterpretation
(laugh with vs. laugh at), but it would certainly mess up the rhythm
of Joey's fine translation.  I was going to use 'cachinnare,' but I
think that's more falling-off-the-sofa, hysterical, maniacal laughter
and that's what I do with *my* brother.
http://www.quinion.com/words/weirdwords/ww-cac2.htm

I hope your brother gets a loud laugh from us stumbling with the
language here.  We always seem to have a difference of opinion on
these Latin questions but they certainly keep us on our toes.
http://www.informalmusic.com/latinsoc

Cheers!
V

Hmm, transitively I agree, I think it connotes ridicule, especially
when it's prefixed by "in", "ir", "ad", etc. (as the case may have
been depending on the era of Latin we're talking about).

Intransitively, though, I often saw it implying simple laughter, being
happy.  I don't know that as such it necessarily brings with it the
qualities of "derision".

This being said, it's hard enough often for me to keep track of
*de*notations of Latin words after a journey of two thousand years, so
it's possible I may have let a *con*notation or two slip by <grin>.

Not that translation web-dictionaries can't be infallible, but the
following seems to acknowledge the transitive/intransitive difference:
    http://www.bible-history.com/latin/latin_r.html

Agreed but since cptlouis indicated some brother *trouble* and with
him being somewhat of a Latin scholar, I thought we'd better *stick*
this verb.  Since I agreed with Pinkie that 'ridemus' could indicate
derision, I ran this around the block looking for another verb or a
qualifier -- just in case.  Couldn't find one.

The only phrase I semi-relevant in my Cassell's was 'ridere convivae,'
but I think that involves laughter, pints of alcohol, a roomful of
Friars Club members, and the barbecued hindquarters of a goat.

When you think of all the nuance in a language -- any language really
-- it's dicey using online dictionaries but I'm backing you up on your
choice here.  The sentiment should be an elegant and uncluttered
translation, which you have, and I think 'ridemus' is the best choice.

Latin questions are becoming like our English grammar questions --
ripe for controversy -- but all in good fun since most GARs are
passionate language freakazoids, myself included.  ;-)

I think your brother will be pleased you went to all this trouble, cptlouis.

Best wishes,
V