Solo is still the more chill way to play Trials. They just have to lower their expectations going into Trials solo if they are not very good themselves.
There are ways they can improve by using easy to use weapons that have a pretty quick ttk etc.. Just depends what they are trying to get out of it you know?
Like, Why are they playing Trials? Is it with the intention to get free loot for casually playing getting them losses/wins regardless or actually trying to go flawless.