For my Velux windows I also use 2 relays, so this may give you some ideas for your blinds.
To start with I made 2 virtual dummy Domoticz Push-Buttons to operate the relays:-
They are defined with scripts to address relays 7 and 8 on an ETH008 Board (This will be different according to your chosen hardware):-
The "Off Delay" is because the relays are providing a "Pulse" and this will return the relay to "Off" after 5 seconds.
I then made this virtual or dummy switch:-
This triggers my relays with this Blockly:-
Note:- I found that "On" and "Off" worked when I created this, but it was a long time ago so with improvements to Domoticz, the "Open" and "Close" options may work just as well.
So that's the basics that I use. You can then go on to automate using further scripting. Here is an example of how I automated my windows. This has developed over the last 3 - 4 years but works really well. (I realise that there are probably far more elegant ways of achieving all of the above and below, however, this all just works for me)
So in Floor Plan I have a timer that sets nominal operating times, the blinds switch, a set-point for opening temp, a position indicator, and most importantly an auto switch that I have on each and every Blockly for when it all goes "pear shaped"

(Or I just want manual control)
Hope this may help you a bit,
Domoticz is awesome.

Domoticz Main - Intel nuc, Windows, RFXTRX433E. Lan Relay Boards, Aeon Z-Stick Gen 5, Evohome HGI80, Milight WiFi, MySensors Ethernet Gateway, Harmony Hub
Python:- Broadlink RM2, Sonos
HA-Bridge - Amazon Echo / Alexa