Before I get into it, Julie & I have had a related discussion under her recent "twinship" question that you might want to check out.
* As to the 49cM case, this shows part the value of having more than one sibling test! For relatives that are 3C and beyond, there's a chance that you won 't get a match. So when one sibling doesn't get the match, the other might.
So what I can tell you right away - since one sibling matches, while the other does not - is that the relation is 3C or more distant. At 49cM it's probably too high a match to be as distant as 5C1R, so I'd say the relation is somewhere between 3C and 5C. Probably something in the middle 4C is the most likely.
* Almost ALL matches in the 20cM to 30cM bracket are at LEAST 3C, so it's not at all unusual to have one sibling match, while the other does not. The more distant the relation, the more likely it is to happen. Matches in this range can be anywhere from 2C1R to 6C1R, from what I've seen.
* 2C1R can go practically down to zero - in fact, there may be a very tiny chance (too small to really worry about) of NOT getting a match at this level of relation. About 1 in 30 of my 2C1R matches are below 20cM, the lowest being 8.5cM. The 2nd-highest 2C1R I've seen on AncestryDNA is 213cM, so your 222cM just sounds like an especially strong 2C1R match to me. My highest is 274cM, but I think I need to investigate that one. If there's intermarrying (which is to say that if the two test takers are related in more than one way) then it throws the numbers off - makes them higher. My 274cM match could EASILY have that going on. The average I'm seeing for 2C1R is about 94cM, so those two are both above average.
If you had just told me 155cM and 222cM, 2C would have been my guess, but I wouldn't have completely ruled out 2C1R. Again, the value is that the 155cM is too small to be a 1C1R while 222cM is too big to be a 3C, so using BOTH numbers you can tell the person is at the 2C or 2C1R level.
* I have a strange gap with the 5 newer tests I have where I have ZERO matches between 76cM and 90cM. My highest 3C1R is about 70 (the same as for 4C, and that makes no sense). So my own data says 105cM should be a 3C or closer, but I question my data on this a bit. On GEDmatch, I have 3C1Rs as high as about 90cM (which is again the same as 4C, oddly). On MyHeritage, I have a 3C1R as high as 96.6cM. Julie reports a 3C1R at 93cM.
So 105cM sounds a bit high to me for a 3C1R, but I'm not really sure. Anything much below that (your 66cM, for example) makes perfect sense. I would think 66cM could be anything from 2C1R to 4C1R.
There's something like a 70%-80% chance of matching a 3C1R, so it's not surprising that they both match.
* 70cM is about the max I've seen for a 4C, so any number between that and zero make perfect sense. The 70cM essentially tells you the match is between 2C1R and 4C. The chance of getting a 4C match is about 46%, so maybe it's a bit lucky for them both to get that match.