Your assumptions are probably correct except Green = Ground. But I never assume when I am replacing switches with smart switches. Get a cheap multimeter and verify everything. Where does that conduit go? Lucky for you the wire is in conduit and if the other end of it is at the circuit breaker, pulling a new wire with a neutral should be easy. Or look into switches that don't need a neutral. If you can't find a single gang smart switch that has two switches in it, replace that single gang box with a double gang and get two smart switches. You have options.
Nope. The multi-meter test is the best idea, but currently the pictures indicate otherwise. Of course anything could be done with wiring, right or wrong, but in this case, chances are:
Blue = Live wire (line)
Black = Load
Yellow = Load
Green = Ground (not neutral)
Take a closer look. The blue wire is common to both switches. That's the hot (line). The black wire is one load, the yellow the other.
You were "not wrong" to assume black is hot. It should have been wired that way. But the electrician chose to use a non-standard color scheme, for who knows why. If possible, when rewiring this get up, you could correct that, at the other end.
Do you actually need manual control of both circuits at that location? You could convert one of those wires to a neutral (at the other end of the conduit) and install one single-gang smart switch at the end shown, and a second single-gang smart switch at the other end.
Otherwise, you can securely tie a rope to one end of all four wires, pull all four out of the conduit, add a fifth wire to the bundle (white) and use the rope to pull it all back through. Use wire-pulling lube on the way back to ease the task.
You could try to pull two wires through the conduit using just one existing wire, but chances are the existing four are wrapped around each other somewhere along the way. Pulling all four out will likely be less frustrating...
But... the electrician used solid copper instead of stranded. Stranded is generally used because it's easier to pull. And that solid looks to be 12 gauge, which will make the pull all that much harder. You might consider replacing all that with stranded, when you pull the neutral.
And if you decide to do that, be sure to use wire that is rated for wet locations. There are (at least) two different types of stranded wire. The wet-location variety would be better for this application. Here's a good read about it: