Property matter (complicated)

I request a good suggestion on this matter from experts. 1) if out of 4 person, 3 invested in a land & name of 4 is mentioned on purchase document & only 1 person made house on that then is all 4 are equal share holder of that land & house or that will be decided as per their investment (no strong proof about individuals investment) 2) 1 brother bought (Not earning at that time) a land on his name (father not alive) while other 3 were 12 years old. 1 brother made his hOuse on 1/2 of that land. 4 of them made house on 1/2 of that land(no strong evidence of all 4 share in investment in house). What will be share in that house? 3) if 1enforced mother & sold 1 land while all other were child, what will bbe effect. 4) if 2 bought land while all were young & included name of all 5 on paper then what will be share? 5) if on this matter 1 share holder became ready with all other on behalf of his family & signed on simple paper partition conditions but now denied. What will happen. Other member may deny but on that moment all other account accepted on phone( no recording) 6) if 1 is treating, abusing others on this Matter what good action may be taken ( very serious & family matter)