I’m helping with inheritance stuff right now for a friend, my only advice: try and clarify things with this notaire, and then get yourself your own notaire so he can check your interests and that you are indeed owed nothing. Seeing your dad was a French taxpayer I think you are owed at least part of anything left in the bank accounts, even though the house is owned by her wife now if they used tontine. Your dad will have done that to protect her from you possibly.
I don’t really trust notaires to bother doing their job properly when you’re abroad (I’m French in the UK, and I’m struggling, even though I hand picked a notaire who is much less useless than most).
You can pick a notaire anywhere in France, in spite of the tradition, it doesn’t have to be somewhere near where your father died.
Signing a power of attorney could just mean that they want to represent you physically for things to be signed more quickly, but these days you can do most things with online signatures with the real paperwork so that’s a little bit dodgy, and notaires are not necessarily as trustworthy as they should be.
If the notaire is harassing you though, it’s very likely because your dad’s wife is harassing them.
FYI the person inheriting the most (your dad’s wife) picks the main notaire where all the paperwork is centralised. It is still your right to take one separately to ensure your interests to anything are checked, and notaires you use for yourself in the middle of an inheritance have a fixed fee defined by the state, iirc it was something like €800 last year.
If you hate her and are sure your dad had nothing apart from the house, and do not want to spend the money, you can just block everyone and they will be unable to go on with some of the procedures for 10? years. Although there must be special treatment for the spouse, I know that someone who disputes stuff/doesn’t reply in inheritance can wreak absolute havoc and disarray, blocking the money for years. I’m also confused about how things go seeing that you cannot be left nothing, it’s against the law, yet a house purchased via tontine isn’t included in the succession. So it is also possible to challenge that the tontine was made to disinherit you rather than protect her from you. Lots of questions to ask a qualified person like a notaire.
Also, you can get some initial help with any notaire for free, some are quite happy to help by appointment. It’s easier to go in person for this but you’ll find someone if you persevere.
Feel free to send me the notaire’s info with all personal details redacted of course, I’ve been deep in that stuff for the past 3 years, I’ll be able to understand why he needs the poa.
As a side note, do not worry, there is little incidence on your side if you do nothing right now, do not let them pressure you (pressuring you and other psychological games is all they have to get you to do what they want). The successors have a duty to fill in the taxes within 6 months after the death, but the penalty for not doing so is a percentage of the tax dues. Seeing your taxable threshold as a child will not be reached, I believe it won’t cost you anything if it’s late.
There’s also a reddit, r/conseiljuridique, where people sometimes ask things in English. Mind scammers getting into your dms because you mentioned inheritance.
I am not a lawyer so please double check what I am saying. These are only a few pointers from my recent experience and understanding.
PS: they may be worried about this:
La tontine est un contrat aléatoire puisqu’il y a un aléa. Pour que la tontine ne soit pas requalifiée en donation, vous devez avoir financé le bien à deux et avoir une espérance de vie similaire. Si ce n’est pas le cas, vos héritiers et les héritiers de votre partenaire pourront demander la requalification en donation, ce qui permettrait d’ouvrir des droits aux héritiers.
Pour avoir une espérance de vie similaire, vous ne devez pas avoir une grande différence d’âge ou avoir un mauvais état de santé pour l’un.
De même, vous risquez la requalification en donation déguisée si seulement un de vous finance le bien ou s’il y a une grande inégalité entre vos apports.
(source: https://www.alexia.fr/fiche/9875/tontine.htm)