Did you mean do them all in one go or one at a time?
Whernside- although the highest is probably the easiest, no scrambling, but can be a slog, although the descent is quite steep.
Pen-y-Ghent- The smallest/lowest of the three but a great walk, steep to start with and a bit of scrambling to get across the saddle and upto the summit.
Ingelborough- My fave! A great looking hill, although the zig zags up the final stretch are quite steep but fun, wouldnt recommend coming down this way. (well i wouldnt want to anyway)
Neither of the three are a massive challenge to anybody of reasonable fitness, but combining the three together is hard work and a slog. But that said the feeling of achievement afterwards is well worth the effort!