Don't quite understand the bolded.
My point is, you're only 1 point behind and you still play them. So you can get past them by beating them. Yes they've got games in hand but they will lose those. As for the other games, you will drop points, they will drop points, who knows. Their run in is not easy.
We do have a six pointer with Arsenal which we obviously need to win to have any chance of securing fourth place.
Let's see if I can do this on the fly:
Arsenal are on 51 points with 12 matches left.
United are on 50 points with 9 matches left.
If we take all 27 points from the remaining 9 matches that takes us to 77 points (please double check my math at any point). Arsenal would need to get to 78 points to hold us off, so if my math is right they need 27 points from their remaining 12 matches. They can lose 3 matches of those remaining 12 and still beat us by 1 point, assuming we win all of our remaining 9 matches. So they'd have to drop another 2-3 points from their other 9 matches, which is certainly possible and perhaps even likely.
But we'd have to win all 9 of our matches. Say we win 7 of those 9 matches, losing only to Liverpool and Chelsea. Then Arsenal would have to lose an additional 2 matches beyond the 3 mentioned earlier plus another draw/defeat to see us surpass them. Anything is possible, but I not only don't see us winning 7 and losing only 2 of our last 9, I also don't see Arsenal losing 5 AND drawing 1 of their last 12.