Short answer. Yes. The rule expressly lists an order or judgment that determines who are the lawful heirs of a deceased person, or the distributive share of the estate to which such person is entitled, among those an interested person may appeal in special proceedings.
What the law says
Determines who are the lawful heirs of a deceased person, or the distributive share of the estate to which such person is entitled
Rule 109, Section 1 — Orders or judgments from which appeals may be taken. Read the full provision →
You do not have to wait for the case to end
In ordinary civil cases the usual expectation is that a party waits for the final judgment before appealing. Settlement proceedings work differently, and this rule is the reason. It identifies particular orders that an interested person may appeal in special proceedings, and a determination of who the lawful heirs are is one of them. So an order excluding you as an heir is treated as appealable in its own right, not as an interim step to be complained about later.
The clause covers two related determinations
Read it carefully, because it does two jobs. It covers an order determining who are the lawful heirs — the question of status, which is the one you face. It separately covers an order determining the distributive share of the estate to which a person is entitled — the question of quantity, which affects someone already recognised as an heir but dissatisfied with the portion allotted. Both are within the same listed category.
Why heirship is singled out
Estate proceedings can run for a long time, and a person shut out at the start would otherwise have to watch the entire administration and distribution proceed without standing, then try to unwind it at the end. Treating the heirship determination as appealable when it is made keeps the question from being answered irreversibly in practice while remaining formally open. The rule takes the same approach to other determinations that fix rights, such as one allowing or disallowing a will.
Act on the order, not on the eventual outcome
Since the order is appealable now, the practical consequence is that the time to act is now, and appeal periods are not a matter to estimate. Note too what the rule does not allow: no appeal is permitted from the appointment of a special administrator, so not every order in the same proceeding is open. The rule likewise excepts an order granting or denying a motion for new trial or reconsideration from its final-judgment ground. It is also worth identifying precisely which determination the court made, since an order fixing a distributive share is a different listed ground from one deciding heirship, even where the two arrive together. Bring the order itself, and the date you received notice of it, to a lawyer promptly.