My brother has three big dogs, two of which love to chase small animals like squirrels.   

Well, you could certainly discourage the squirrels from burying the nuts on the site by various means-- and I definitely would do what you can there if you plan to spend much time there.    I don't suppose that you can have a dog?

No need to challenge hazelnut - we know 100% that it leads to anaphylaxis via a very clear reaction history.  Plus, the thought of any sort of peanut or nut challenge is enough to send my PTSD spiralling into the danger zone.

I guess we'll take it as it comes.  Dad is for sure cutting down the hazelnut trees on the property (whilst I am not there).  We don't have to leave their property if nuts are problematic in the surrounding area.  And people think people with food allergies only need to worry about what they eat...

1.  No--and we live in a prime growing region-- but then again, DD isn't allergic to hazelnuts, and we know this via a challenge (which I'd recommend if you're eligible for one).

2.  Yes, I'd be VERY concerned about that-- there's not much way to keep the squirrels contained.

My parents just bought a new-to-them cabin on a beautiful acreage lot.  The one big red flag for me its hat the previous owners said there are loads of hazelnut trees on the property, and that the squirrels like to eat the hazelnuts and leave the shells around.  That sounds all lovely and beautiful until you realize you are super allergic to hazelnuts.

My parents have prioritized two items upon possession: build a fence (for my brother's dogs) and cut down the hazelnut trees (for me).

1. Has anyone ever had problems with hazelnut nuts and shells around hazelnut trees?  I'm thinking of Mac(?)'s recent experience with squirrels leaving peanut shells in their garden.  Seeing acorns on the ground in my neighbourhood makes me anxious but I don't have any reason to believe I'm allergic to acorn nuts. 

2. Will spending a great deal of time in an area where hazelnut trees are prevalent (on other lots and in the nearby woods) be problematic?

Just wondering what you think.  I'll add this to the list of questions to ask my new allergist when I see him this autumn.  (That appointment cannot come soon enough.)