I WOULD NOT agree to this. I'm a MB. I've had two under two three times. There is no way to watch both children like a hawk all the time.
They will apologize profusely when something terrible happens, and you will just have to hope there are no permanent injuries.
An exersaucer, pack n play, or the like will only work for a little while until they start climbing out. You need a solution that will continue to work until they are old enough to somewhat trust (2.5? 3?).
In the meantime, something like this will work (you need a tall one; I'm not sure how tall this particular one is):
https://jet.com/product/detail/b0670da704fb40e6bff40ffdef94199b?jcmp=pla:ggl:gen_animals_pet_supplies_a1:hn_pet_supplies_pet_playpens_a1_other:na
LA_345544740_24784133100_pla-173070444300:na:na:na:2&code=PLA15&ds_c=gen_animals_pet_supplies_a1&ds_cid=&ds_ag=hn_pet_supplies_pet_playpens_a1_other&product_id=b0670da704fb40e6bff40ffdef94199b&product_partition_id=173070444300&gclid=CKbfsOfDxs4CFVY6gQod3qYFnQ&gclsrc=aw.ds