Older sister ? If she is older then he might be just copying her, if not then there might be a deeper psychological problem, have you spoken to him ? AT 7 years old he is at an age where he should be able to talk to you about it, try talking to him we must always try as much as possible to talk to our children about everything.
Don't wear underwear.
A 10 year old boy should wear underwear to school and everywhere else. Underwear serves as protection.
Briefs
You should make a list of the pros and cons, plus why you want to wear girls underwear. As a 12 year old boy, you will need to make your mom understand why you do not want to wear boys underwear.
If you like to do that you are probally gaye. I advise talking to your family and maybe going to a therapist.
Of course it is. In fact, a 14 year old should wear underwear or panties. They support the rear and also shape them up so they do not become rather, well, saggy. So, yes, it is very much okay for a 14 year old to wear underwear or panties.
panties
If the 12-year-old is fine with it himself/herself, then yes. But be aware of the infections and deceises it might come with it. A 12-year-old should not be forced to not wear underwear, as most people feel more secure when wearing underwear. Do not take that secure feeling away.
Whatever he's comfortable in.
You could tell your dad you are a transsexual or you have a gender identity disorder. However, he may get angry or send you to therapy. This may not be worth being able to wear girls underwear.
make them wear "goodnight" pull up underwear and not let them wear big girl or boy underwear until it stops
No! Kevin is too old to wear flower underwear. Besides, flowers are girly.