12 & 14 act like 5yr olds - how to discuss with mum

[~ Zarava Flutterby ~]

My mum, step dad and 2 brothers will be moving to Adelaide in the next week or so, i have had my 2 brothers here for a couple of days and notice their behavior more and more.
We (DP & I) have always noticed they act younger than they are for the following reasons:

1. They are hard to have a conversation with - they talk slowly, about things people are not interested in, forget what they were saying half way through and then start the conversation 30min later when you have no idea what they are talking about.

2. They are VERY affectionate towards each other and other people, they will lay on each others knees and rub their hair, they always kiss and cuddle everyone before bed (have started shaking guys hands now though), constantly trying to pick DD up and baby her when she sooks or comes near them.

3. They literally act like 5yr olds, were in the pool this morning and they were squealing and acting like little kids, even DD doesn't squeal like that in the pool.

4. You tell them to do something and if they are watching TV they are oblivious to the world, you have to near on yell at them to get their attention and even then they look at you blankly.

5. They hardly hang around kids their own age, they never GO OUT and hang with friends, they don't go to the movies or catch buses anywhere.

I am seriously worried they will move and someone is going to belt the crap out of them, they both play sport and have plenty of interaction with ppl but they hang with mums friends kids (always seem to be the feral clingy type, mum gives a lot and gets nothing in return).

I want to chat with mum and tell her she REALLY needs to let them do things for themselves, they need to go out and experience life and grow some balls (so to speak), spend less time relying on each other, mum and her friends and do something for themselves.

The 14yr old can basically get his L's when he moves, we told him this and thinking most young boys would LOVE that idea he went pale and looked petrified, i said he could have his licence by like 16 or whatever and have some freedom and he almost looked like he would cry!

Also just remembered while they have been here they sit and watch DD's cartoons and they are transfixed, i have to tell them to turn the TV off and go outside or do something else.. DD only watches telly til 10am (even then she's playing not watching) and then it's off and she plays inside or out.
I have had to tell them about 15times not to jump HARD on the tramp as it's not ours and has special springs for smaller kids.. this morn the oldest B jumped really hard and i spat it told them to get the F off it and their not going back on at all... i felt horrible but seriously how often do i have to tell them?
They play with DD's toys even when she's in bed and otherwise all they want to do is play the playstation all day.
We are on 10acres, not once have they asked to ride a motorbike or just gone out to explore the paddock, they could take the dogs for a walk, go on go-karts, chase lizards.. NO NOT INTERESTED!

By this age we were hardly ever home, doing things on our own and very independent... how can i bring this up with mum?
Sorry it's so long but it's really getting to me, my other step brothers are 8 & 6 and behave better in public and have better social skills.