1. Assuming that your elder brother, who was a bachelor, died intestate (without executing WILL), then as per the Hindu Succession Act, your deceased elder brother's property would devolve equally to his mother (if alive) and all his siblings.
2. In the instant case, assuming that your mother had predeceased your elder brother, then the property would devolve equally to younger brother and three sisters, i.e., 1/4th each.
3. As narrated by you, two sisters have executed Gift Deed in favour of younger brother as also one of the children of deceased sister has also executed Gift Deed in favour of younger brother. Except one child of the deceased sister, all have executed Gift Deed in favour of younger brother. If the Gift Deed executed by all of them is adequately stamped and registered in the jurisdictional Sub Registrar's Office, then it's in order.
4. Regarding the remaining legal heir who is in Canada and untraceable, you can obtain Court Order from the jurisdictional competent Court, since he is untraceable and has not made any contact for more than 7 years. In the instant case roughly for about 24 years. Court may likely to consider your prayer to collect rent from the portion of the property which has been let out.