Wiring up the switches is pretty basic, but describing it in words is probably a little complicated. They are called 3-way switches. If you do a search for that term, or go to a book store and look at a book on basic wiring, you should be able to find a diagram.

As far as daisy-chaining the smoke detectors, I believe all of the smoke detectors have to be the same brand. Look at the instructions that came with the detectors.

In some places, you HAVE to daisy-chain the smoke detectors, and they should have a third - yellow I think - wire which makes all detectors go off, if one does. Check your local codes.

If you don't know how old your detectors are, better to replace them anyway - the radioactive isotope they use has quite a short half-life, and they won't function once it decays past a certain level. Newer detectors have a use-by date on them.

The detectors not only have to be the same brand they have to be compatible models. That will be listed on the boxes or on the manufacturer's web site.

Two switches for one light requires two "3-way" switches and a 3-wire cable (with ground) between the switches regardless of whether the power is to a switch or the light fixture. The white wire is treated as if it were black (and marked as that). If you don't clearly understand how to wire the switches, ask someone who does to do it for you. Don't guess and risk causing a fault.

Here is a link that might be useful: 3 way switches