Do you have some kind of time constraint? In other words, do you have to have all this done in a month, 2 months? More?
I’ve never had to declutter my own stuff although I feel like I should do a bit of that as I accumulate more stuff. I tried to do at least some decluttering at my parents house after they had passed. That was a bit trickier because I had to worry about if my siblings wanted anything, although they couldn’t be bothered to help much with the process.
I like @kritiper ‘s suggestion that if you have big bulky items that you no longer want, get rid of those first. One of the things that really helped me when I was trying to get my stuff packed up to move was when we finally got rid of my parents old piano. (We had had a tuner come out and assess it and he let us know that there was tons of work that would have to be done on it, as my parents hadn’t kept up on the maintenance or had it tuned in 50 years.) Once that was out of the way, that gave me a fairly large corner of the living room to start stacking stuff. So if you can get rid of some big items, that may allow you to spread out a bit more as you go through everything.
I understand you want somebody to help you organize, and if I lived closer I might come over and try and help for a nicely cooked meal. But I myself wouldn’t want somebody coming in to help me because sometimes people want to force decisions on you and rush you through the process, and only you know how much time you need to go through things.
If you don’t have any time constraints, maybe just set a goal for yourself of getting rid of a trash bag or one box of things a day and hold yourself to that. It may take a while, but as you work you will probably get more of a sense of where you want to go with what you are keeping and what you are getting rid of and it should get easier over time.