Tip is a little bigger on the left than the right (left shoulder more developed, left haunch higher), which isn't unusual. All horses (like all people) have a preferred side, and that side will be more muscular (and often less flexible - they'll bend to the left with no problem, but going to the right is tougher because they have to stretch that muscled side). From a saddle fitting standpoint, it's not a big deal unless this is a chronic issue that won't be changing, and then we'd most likely deal with it through flocking adjustments. However, I'm guessing that this is a stage he's at in his development, and it will change.
Though it's hard to tell for sure without a tracing (or without getting my hands on his back), I think Tip can be fit with a fairly generous standard tree - I don't think a hoop tree will be necessary; he doesn't appear to be that broad through the withers. Again, a panel with a fairly shallow gusset would offer a nice broad weight-bearing surface for his nice, broad back without making it sit too high in the cantle.
Now for Tip's sides:
This looks pretty straightforward - no major dips or divots (small one below the wither on the left side), so probably wouldn't need wither gussets or a trapezius panel (can't tell for sure without a tracing). So, based on the photos and Renn's description, my recommendation would be a Black Country Quantum. Since Renn's femur is about 14" and the Quantum has a flap that will accommodate a long thigh, a 16.5" seat might work, or perhaps a short flap option would be worth investigating.
Some other possibilities for Renn and Tip would be a Frank Baines Reflex cc, a County Stabilizer, or one of Albion's close contacts.
Renn, thank you so much for being the first. And if you'd care to send a tracing, I'll make further recommendations.