As mentioned, Holy Cross is a strenuous one. Here is a story about our first attempt (which was with people who had impressive climbing resumes including on the highest peaks on earth):http://www.summitpost.org/mount-of-the- ... mpt/170788
I doubt that any guide is going to take you up El Diente unless it doesn't snow much between now and then.
Also, your post seems to indicate that you have only two days? Unless you are an very strong climber, planning on two days isn't really realistic for those peaks in full winter conditions.
Because Holy Cross isn't that technical, it probably could be done by a novices with strong leadership/guides, but you should plan more than two days for novices. Even for strong and in shape novice climbers, I wouldn't recommend it without winter experience or a guide because if you stay on route the route can be fairly safe, but getting off route will lead to trouble quick.
It is snowing now, but so far there is hardly any snow in the mountains, so I guess if that continues, it may be theoretically possible to climb those peaks in non-winter conditions by then.