1) you , your mother and sibling have one third share in the house
2) on redevelopment it is advisable to negotiate with builder to get 3 separate flats rather than 2
3) if your mother name is included in your flat on mother demise intestate ie without a will your brother can claim share in your flat as he would be one of legal heirs of your mother
4) it is possible for mother name to be included in both the flats
5) mother can execute will bequeathing her share in 2 flats purchased in joint names to you and your brother respectively