Well...flaked barley is just barley that's been sliced and rolled flat like Quaker oatmeal. Pearl barley is just barley that's had the husks and bran removed, so it should substitute just fine. To use pearl barley, I would crush it up pretty well and then mash it. Good luck. Let us know how it works out.
I asked the same question last week. I think you need to cook the barley before adding it to your mash. My LHBS said boil it for 20minutes then add it to the mash.
I ended up needing some other stuff so I went to another LHBS and got the flaked barley there, so I can't tell you if it works but I reckon it would, it's in the Complete Joy of Home Brewing, too.
If you are planing on a partial mash, then you will need to replace some of the DME with more 2-row. But with those grains I think you can get by with just a steep if you get rid of the 2-row. Steeping 2-row won't properly convert it, and will leave your beer with a starch haze.
yah 2 row is the barley, two row yields high sugars in your mash and should comprise most of your grain bill if you plan on using carapils. +1 Barley water, you are most likely going to need to mash.. Go all grain its awesome