Just to give you some information.
1. Legal Separation means that a husband and wife can live separately but are still married to each other. In relation to the new kid of you dad, he/she will be considered as an illegitimate kid and only entitled to half of your share of your legitime as heirs of your dad.
The properties of your father MAY be transferred to other people if it is by way of a sale. If it’s via donation, it must not affect your share of the “mana”.
2. If there is a decision for Legal Separation then there is a guilty spouse. The guilty spouse will then have no rights over the net profits of the conjugal properties of your Mom and Dad. Better check if there is a decision regarding this as said by your Mom.
3. Better consult a lawyer for any action you can file against the transfer of the properties of your Dad to his new partner and kid.
