DTV_BegPecker income amount doesnt matter

You apply individually. Most embassies don’t require the children to have money in their account, but some sort of support letter from the parent with the bank account. For the spouse, some embassies require a total of 1 million while others don’t. Also, once your oldest child turns 20, I don’t believe they can apply as your dependent. Since you plan to go in April, you would apply in Feb/March. Hopefully the child is still 19. However, it still could be an issue, being so close to 20