For Barcelona to overtake Real Madrid at the top of the La Liga table and end up winning the La Liga trophy this season, they need two things to happen: to be consistent in winning their matches and for Real Madrid to continue losing points. The chance for Barcelona to win the La Liga title this season is slim because both things cannot happen at the same time.
After 26 rounds we have difference of 8 points between Real Madrid and Barcelona which is currently at the 3rd spot and now in 27th round match they are going to visit Bilbao which is also having impressive performance in home games and Real Madrid is going to visit Valencia with in 26 matches they lost only one and Barcelona already lost three which is making good difference even we can't predict about anything in soccer specially while we are heading for the end of the season but for me most chances title race is already ended for the Barcelona with now they are doing their best for having second spot which is also not bad for them with too many on and off the field issues which are creating problems for them.
First they need to end their financial issues which are preventing them from having new and quality players which bring good improvement and consistency if they want to win La Liga in coming season, otherwise things can go from bad to worse for them as well.