hey dude... As others mentioned.. your minimum basic should be 7500 Qrs to apply .. But these days there some elaxation if the company says in thier letter that they will provide you with family accomodation...
You can combine both the salries and make a good statement with the help of your company if they agree to take your wife salary and deposit it to the bank on monthly basis for atleast 2-3 months....
Regarding your son.. I would say its better you apply for Residence visa before bringing him on visit visa... Otherwise its too risky and not sure.... Do Not compromise on his education unless you are sure about residence visa...
Best of Luck