Wishbone rear mounting bolts change

Hi,

I got this bolt so rust that they snapped off. Problem is that i don't know how i should change those ? Are they welded on body or what… 

Yes they are welded to the car, its a bit of major work to replace them.

Can i drill them out and put normal bolt, so that bolt head is inside on body ? Is there hole or something where i can get access inside of body ?

Never done it or sure how to but lots of info on the web like this,
"There is a strengthened plate inside the box section that holds the studs. Cut it open from the side to drop a high tensile bolt in after drilling it out. Then weld it into position and weld the box section closed."
Sounds easy !!Some pictures in the thread here showing inside the section so you know what your up against..
http://www.clubgti.com/showthread.php?241545-repair-for-mk1-golf-rear-axle-mounting-point

http://sciroccoregisterforum.co.uk/faq/2010/02/22/repair-rear-beam-mounts-scirocco-mk1golf/

Info in Haynes manual as well.
You need to make sure its done properly as those two bolts each side are the only things hold the rear wheels to the car! 

the haynes/bentley way (and thus, the VW way) is to grind flush, then drill up into the remains and tap it out to 10mm thread. then use a 40mm 10.9 grade bolt.

however that being said if the chassis is all grotty there and full of holes anyway then you may as well chop it all out and weld in a new stud