Regarding #1, see my Mac Malware Guide.
As for #2, note that there is no malware for any iOS device, except for devices that have been jailbroken. So security in general is pretty good, though you've got to worry about potential privacy issues with individual apps or how you use your phone (like whether your photos posted to Facebook have location info embedded in them, etc.), phishing attempts in e-mail, questionable web sites, etc. All these things are issues for any electronic device that connects to the internet, regardless of platform.
As for #3, your Macs are almost certainly clean if you have kept up with all updates. (If you haven't, run Software Update ASAP, as there's an update that can remove one piece of malware that's going around right now.) However, if you want to scan it for malware anyway, after reading my guide, you can use Sophos Anti-Virus for Mac Home Edition or ClamXav, both of which are free.
(Note that my pages contain links to other pages that promote my services, and this should not be taken as an endorsement of my services by Apple.)