Aww please don't kill them, they just don't understand.

When my dog and my Mum's dog were living together we had the same problem...and you have two VERY food orientated breeds with a Beagle and a Boxer!

Do you have time to feed them one at a time and make one sit and hold him/her by the collar (or even give it a pat) while one eats in peace, and vice versa? This is what we did for my dog and my Mum's dog and eventually we didn't have to hold them anymore.

Eventually they will realise that they actually aren't any real threat to each other's food. At the moment it seems like they see it as a survival situation and don't realise that they are BOTH going to be fed. It's a heirarchy thing that they are trying to sort out between themselves but unfortunatley as you said it could be dangerous for your family.

Also your Boxer is still a puppy in the head. They are notoriously slow to mature mentally, as was my Labrador. At 3 years old she was still really hard to handle. A lot of larger breeds take a bit of extra time to 'grow up'.