Read the article. It's full of all the information you need to brood outdoors and then integrate the chicks with the adult chickens.
I would move the older chicks and the two new babies out to your coop/kennel right away. Of course, if it doesn't include a secure, enclosed hen house, you're sort of out of luck. You do need for the chicks to be completely sheltered from cold drafts, rain, and predators.
My system works best if you brood right alongside the adult chickens, not wait until the chicks are six weeks old as "conventional wisdom" dictates. (I ignore conventional wisdom every chance I get.) The theory is the adults come to accept the chicks early on as part of the flock, so when they begin to mingle with the adults, there is almost no aggression. And with the panic room system, the chicks are guaranteed a safe have if there is any attempt at bullying.
To clarify the heat weaning process for your soon-to-be-three week olds, you need to watch their behavior and as they tend to hang out farther from the heat lamp, then you decrease the heat. Also, on nice days, you should be taking the older chicks outdoors for brief periods to get them used to cooler temps, increasing the time each day. This encourages feather growth, and by four weeks, they are usually feathered out enough so they will only need maybe a 100 watt bulb for heat at night.
Your new babies will not need a heat lamp at all. They will wean themselves off the heating pad as they grow, and you will know they're weaning when you see them spending more time away from the heat cave or on top of it. Please join that thread and they will be thrilled to take you under their wing, (notice how many chicken metaphors we have in our language?) and help you to set it up and understand how it works, and with any problems you might run into.
By the way, the articles are again listed right below this post in blue type, indicating they are hyperlinks to the article section of BYC.