Getting to Three Brothers Peak is one of longer treks to a Teanaway summit but, like most of the others, it has expansive views of Mt Stuart, surrounding peaks, and on a good day Mount Rainier. I have only done this peak in combination with Navaho and Freedom (aka Little Navaho) Peaks - that trip was 14.2 miles and about 5700' of gain according to my GaiaGPS track. My Gaia user name is PNWRich and all of my tracks are public so you should look it up.
Most of the work is getting up Navaho. From there travel SW toward TBP then head off the Navaho massif when it looks good. Once down in the basin between the two just take the easiest way up. There is a bit of a trail but you can just slog up it whatever route works best for you. There are several ways to get back to the TH - but I'd recommend hitting Freedom Peak while you are all the way out there. It's actually the shortest way back, it's a great little peak, and I have another hide there. :)
You'll need a NW Forest Pass if you park at the Stafford Creek TH. If you are hardy enough to make it all the way to the summit then you shouldn't have to look too hard for this cache. I've made the hide fairly easy - it's just south of the summit. Use your geo-sense and you'll have no problems getting the grab on this small lock-n-lock container.
While this peak can be summited all year long you only be able to get to this cache when the summit is free of snow. Whatever time of year you go please make sure you are prepared and know your limits. Have fun!
Congrats to Ms. Marvelous for the FTF!!!