Kitchen Remodeling Question

Without knowing what the whole structure looks like (how it's built) it would be dificult to predict. I would enlist the help of a competent building contractor.

I agree, find a professional. We know far too little information to give any acceptable answer. we can only make numourous assumptions from the information given.

If its on the ground floor, can't you put a supporting wall under the beam, where you know the load is heaviest?

I think builders refer to them as 'ghost wall supports' or something.

If you are replacing beams and are unsure of what to use then it would be best to get professional assistance. For the cost of the home, the time it takes to fix and the amount of damage that could be caused by not supporting load bareing walls properly. It makes sense to do things right and by code the first time. Any knowledgable contractor should be able to quickly identify what you need to do. I would also have in a building inspector to look over any work that you or a contractor has done.