Assuming that your brother and his family will be car camping, you might want to suggest something big and versatile like the
REI Kingdom series. They're kind of cool because you get a nice, big space with some netting too. I've had two REI tents that I love and borrowed a big 6-person one from a friend for over a month in 2012. Big Agnes is another solid manufacture, as suggested above.
Depending on the ages of the kids, he might want to consider one big, main tent and separate, smaller kids tent. Or another option might be a big tent and a mesh bug tent for the nights when the mosquitoes are biting.
No matter what kind of tent they buy, make sure that the salespeople set it up with him at the store. The three outdoor stores I shop at all have their sales people walk you through the setup process, and give you tips and tricks. For example, sometimes you will need to buy extra guylines or better stakes. At some campsites with hard ground a plastic mallet can be the difference between a nice, tight staking job and a frustrating, painful task. Whatever you do, you do not want his first time setting up a tent being at dusk at the campsite.
If any other questions come up, ask away! If he's thinking backcountry camping, that might be a whole different set of questions.