Actually, the situation right now with respect to the position re: independence is very much the equivalent of a two-party situation.
“Together for Yes” is an alliance of parties, not a single one, whose only point in common is (theoretically) wanting to get an independent Catalonia. I mean, in “Together for Yes” you have urban bourgeoisie rubbing shoulders with Venezuelan-style revolutionary socialists…! Honestly, I strongly suspect that if they ever managed to really get in power and really get an independent republic, the next thing they’d do would be to rip each other’s throats with wild abandon.
The other side is firmly against independence, and would seem to be coalescing around the “Citizens” party. This side seems to be more ideologically coherent overall, though.
Those are the two sides that are shaping to be facing off this coming December.
Now - it remains to be seen whether the coalition that went as “Together for Yes” last time will run again; it seems that the inherent tensions within the group are beginning to raise their head. ERC (independentists left of center) may well consider that PdeCAT (kinda-sorta-independentists right of center) have become an electoral liability (PdeCAT -or rather its predecessor- is the party who basically set everything in motion years ago, very likely as a maneuver to distract the people that ran out of control) due to the mess they have made of things (Puigdemont, he of the bipolar wavering, is from PdeCAT). And then you have the CUP, revolutionary socialists crazier than a March hare who ended up at the top riding a wave of angry voters who wanted to punish traditional parties and who are a bunch of intransigent maximalists always shouting “my way or the highway” (one of the leaders of CUP made a charming declaration basically amounting to “Parliament is useless”. These guys are all for a revolution or something; ironically a lot of them are idle kids from rich families, possibly playing at being Che Guevara).
If they go separately to the elections, instead of presenting a unified list, that will hurt their chances (due to the D’Hondt system for proportional voting in use).
Whether the other bloc will unify or not, that remains to be seen. However, were they to do it, I think their internal stresses would not be so high.
EDIT: CORRECTION (but I am leaving up my wrong text above): “Together for Yes” is made of PdeCAT and ERC; CUP is an external support. That changes my analysis; the internal stresses inside “Together for Yes” are less serious than I thought. However, I still feel that PdeCAT might be considered to be a liability by its partners. Also, I think that CUP, running on its on, would basically collapse in the next elections -or, at least, would lose a lot of support.