For now even I'm not sure they can beat PSG even with their good form at the moment.
Their biggest chance is to secure a draw and this they can still maintain but to win this will be very difficult although it would be good if they can win because at least there is still a club that can hold PSG to remain competitive .
Marseille and PSG when viewed from the results of eight matches this season are still both unbeaten, only Marseille have drawn twice so that PSG is ranked first in the standings at this time and it can actually still be won by Marseille from PSG if Marseille is still able consistent throughout this season, including having to be able to beat a PSG team that is still very strong in Ligue 1.
Although there is still a big chance for Marseille to win the Ligue 1 trophy this season, and the difference in points with PSG is not too far away.
As you said, Marseille is able to play consistently until the end of the season and can beat PSG when they meet PSG. So they can get the Ligue 1
trophy winner, but unfortunately the reality is not that easy for Marseille to make this happen. Moreover, Marseille does not have the quality of
players like PSG, so let alone beat PSG, playing consistently until the end of the season I doubt Marseille can do that. It must be remembered that
there are still some strong teams in Ligue 1 who have not yet faced Marseille, so there is still the possibility of Marseille dropping points in the next
few games. My prediction is that PSG will win the Ligue 1 trophy again, it is too difficult for Marseille to end PSG's dominance in Ligue 1.
Moreover, I see PSG's performance getting better since Galtier became the new PSG coach.