Alright so I agree with the idea of limiting what can be summoned, I also like the ideas you suggested for hp. I think going forward I will be doing their hp in that style of x d y + cha (x being level and y being dice value) Possibly as an additive for the flavour I am considering it being creatures of intelligence, less so in a stat sense and more so in a sense of if that creature would be able to comprehend a higher being the master.
Rebirth Ritual I am still uncertain of how I want to take it, as I feel a mechanic to buff summons is needed for later game, however in its current form it is very strong and cheap, I like your concept of having fallen companions becoming a damage buff similar to smites. To detour slightly, whilst writing I had the thought of having the ritual be ways to unlock new abilities, so for example a Knight Soul may be able to unlock a smite ability costing some embers to obtain, and then maybe using your sorcery points as a cost? This feels interesting to me, however I am unsure on how balanced it would be, again its a spur of the moment idea.
Rapid Summoning and Symbionic resonance I think would be nice to have free uses up to your Charisma modifier before costing sorcery points to use, at least per long rest. I also agree on reaction for Symbionic resonance and will add that.
I agree with umbral convergence, and will add a note of it only affecting those you target, I probably will also add a sorcery point cost to this after you use it once or twice for free.
Leigons of souls will be getting play tested by me in an upcoming campaign where I playtest the whole sorcerer and do tweaks for gameplay, so I cant say much on it right now.
Agiphael I think will get their own stat block, and will most likely have the combined hp of both components, I might consider doing a few variants, for the spice of fusing a Knight with a Witch, or a Beast and a Ranger, I think that would add the most flavour.
coarse torrent
shrewd wyvern
