1. There was
never a separate dependant visa route for dependants under each part of the PBS system at all. This is a common error. Under the old PBS system, there was just one PBS
dependant route, so all dependants under the PBS system were issued visa under the same exact route
Needless to say that under the long residence route to ILR, any combination of visas can be included (apart from some visas like tourist visa, etc)
2. No, they cannot get ILR as child dependants unless
both parents are either settled or settling with them. However, they can apply under the long residence route if they qualify on their own. In your case there might be a better way, as I explained below
3. You getting ILR has no effect on their visas. It seems your spouse has been your dependant since 2016 which means she is also eligible for ILR the moment you get ILR. They can all settle under
the skilled worker route, assuming your spouse meets the absence limits. The fact that you settle under the long residence does not matter.
See:
ILR clock does NOT reset for skilled worker dependants when the main applicant settles under the long residence
Advice is given based on my personal research and experience only. Do NOT contact me via private message for immigration advice