I expect you will go back to the grave many times after the funeral...not to say goodbye but just because...
the funeral is just society' way of trying to say its ok to be sad but you are still with the living and in the great scheme of things it may well be less important to you and your OH than the grandparents etc. I would let them come but ask them to stay away afterwards so you can go back knowing you will have time and space on your own... and alsoask them to avoid going on the anniversary
what ever you decide will be 'right' at a time when the whole thing feels so very wrong