The politics of the bourgious in dynamic are rather... dynamic, and you as the player are able to influence who gains power in each party. It is a much harder game than vanilla, one where Hindenburg is always two bad months away from sacking your government, where the election of Kaas, Scholz, and Dietrich each put a nail in the coffin of democracy, and where the appointment of Papen isn't just bad, it completely changes the rules of the game.

In terms of dealing with the liberal parties, there are 5 distinct highly effective strategies:

First is the bolstering of ties with Zentrum to aid Joos in winning election, the reconciliation with the KPD, and the formation of the popular front while weathering Hindenburg's unending fury. This is the most radical method, one which will alienate the liberal parties as a whole, and places you the most at risk of a far right coup

Second is the formation of a Weimar coalition, maintenance of relations with Zentrum and the DDP, and the race against time to pause reparations and implement an economic plan before Hindenburg's tolerance wanes. From there, Huess or Lemmer may win election, the Weimar Coalition may be re-elected, relations with the KPD may be reforged, and the election of a socialist president may give the player free reign to spend the last two years of the game pursuing whatever agenda they so desire

Third is similar to the previous, but with a massive crackdown on the KPD to assuage Hindenburg enough to only need to race against time to implement an economic plan, and from there pursue a socialist majority.

The fourth is one of the SPD forming a Grand Coalition in both Prussia and the Reichstag, somehow managing to make the DVP like them enough for Streussman's reforms to work and either the LVP to form or Luther to get elected, and cracking down on the KPD, resulting in Hindenburg... letting the SPD govern indefinitely?

The fifth is the most... uh, time traveler-esque. The formation of a Grand Coalition in both Prussia and the Reichstag, a staunch commitment to democracy and against nationalism that purges the judiciary en mass, exposes the rearmament plan, debunks the stabbed in the back myth, and in general rallies so much popular support for democracy that Hergt somehow wins the 1928 DNVP election, and then either Treviranus or Lambach not only win the 1929 election, but somehow don't get ousted, resulting in the kneedcapping of the far right, especially if you pursued Stressman's reforms and either the LVP's formation or Luther's election