From my point of view, these rules are reasonable, but I doubt the parents will agree. However, by next year the children will be a year older and their parents might just have reviewed their ideas.
Send your ground rules by all means, but please discuss now with your husband what you both feel the outcome should be if the two sets of parents are deeply offended when you do so.
Make sure they realise their father is on board with your proposed solution.
I would buy 5 identical, unbreakable, cheap plates, soup-plates and mugs for the children and set the table with these. if the whole family is coming.
The children either eat and drink from these plates and mugs, or leave the table, but no substituting a different plate.
In your place I would concentrate on food being eaten at the table as served, and not make rules about toys being played with on carpets only, if you live in a house. In a flat with downstairs neighbours, obviously the rule about not playing with toy cars or bricks on the uncarpeted floor is wise.