Erm, Chelsea and Spurs have both lost two of their last four games. If we went the rest of the season without losing a match of course we'd be in for 4th. We're only four points of 4th as it is.
Lets assume they keep that up then. Chelsea have four points more than us and eight games to go, they'll lose 4 and win 4 and so get 12 points. That'll leave them 16 points ahead and we'll get 14 from winning our home games and drawing the aways. (Obviously that requires them to lose a game against us that we've drawn, like but a point extra to them makes no difference.)
Same with spurs, seven games left and six points ahead. They only need to win three and lose three and draw one to finish above us if we don't win any aways.
We have to win at least 6 out of the 8 to get 4th, which is 3 away wins out of 5 and is going to be some task.