I'll try my best but please don't be offended if I miss something, covering every detail is difficult.
Vorrindor: Trading with the Eutemas Patriarchy, Lotharine and Cherawyn. Robert Herrin is betrothed to Eva Solari of the Eutemas Patriarchy. Vorrindor is currently supplying the Mercer Supremacy with troops and provisions to help them unite the central kingdoms (The Blackveil Covenant, the Patels and the Supremacy).
The Patriarchy: Currently trading with every major civilization on Rotafar. Eva Solari is currently betrothed to Robert Herrin, heir to the Twilight Throne of Vorrindor.
Sondheim: Still recovering from a slight victory in its civil war, Sondheim is yet to erect any trade links with other civilizations apart from the Patriarchy, due to their focus on rooting out the last of the Scar-Bearer rebels.
Lotharine: Currently trading with Vorrindor and Cherawyn, Lotharine cut off trade connections with the Patriarchy due to their condemnation of non-human races like Harpies.
Cherawyn: Cherawyn has remained elusive thus far, trading with only Vorrindor and the Patriarchy to this point.
The Mercer Supremacy: The Mercer supremacy currently trades with the Patriarchy and is the only Kingdom currently in open war. Backed and supplied by the Kingdom of Vorrindor, their current aim is to unite the three central kingdoms into a single Supremacy.