Too many steps to answer here, go to www.parktool.com, www.sheldonbrown.com or www.bicycletutor.com for more.
put my mum on the seat and grind
Change the wheels with specil ski wheels i think its called ski bike.
A 20 inch tire.
axle mounted, yes.
It´s the Stem, it holds the bars and match with the frame with the help of a headset.
Yes, pegs can be put on any BMX Bike. You will need a socket wrench to put pegs on certain bikes how ever.
Depends on what's already on there, what's available, and how much clearance the bike has at the fork and frame.
u could cut it up then make all the bits smaller and then put weld it back together again
No, you cannot put pegs on a mountain bike for stunts and tricks. Mountain bikes are not designed for this type of use and adding pegs could compromise the bike's performance and safety. It is recommended to use a BMX bike for stunts and tricks instead.
Not a sprocket only, but you can buy a 23-tooth freewheel that should fit.
I'd say no. It has suspension, which makes it heavy and sluggish in handling. It also has an externally geared rear hub, which is likely to get banged up real quick during the kind of use BMX bikes usually have to put up with.
Probably. Today BMXes can have either a freewheel hub or a cassette hub, but as long as you stay within the hub type you can move parts from one bike to another.