You would want to get expert opinion

2 boys are not a lot of weight - until they are 6 ft tall :-)

But it is better to put in extra caution.

Most landlords are not structure experts, so our opinion will not carry too far. You want to consult with real experts that actually see and measure your place.

Try to find 3 groups of companies:

1) The top ones in your area. These usually are most expensive but technically sound. Get written estimate from them. - From this group you would know what is the most sound approach and what is the upper limit of cost.

2) The cheapest ones (but may still be still licensed) in your area. Get written estimate.

3) Work with mid-range contractors to get estimate. Use the written estimate from the 2) group and ask the 3rd group to match or beat them.  This is your target group for actual work.

Now you likely will have the best knowledge of scope/design and possibly best pricing as well.

I wouldn't worry too much about paying slightly more than what offered by the 2nd group. (i.e., don't push the envelope too much to break the negotiation)

For each group, get up to 2 quotes to have a better vision.

This approach is useful for larger and more (safety) critical project. Smaller ones, you don't want to spend a lot of time just for getting the right quote. - Just do it will be just fine.

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Light is one consideration, volume and elegance is another. But if you need space badly, I guess space is more important.