I am certainly no expert on this but we raised our two babies as puppies at the same time (boy and girl litter mates). We also read similar warnings on line about what a terrible idea it was to raise two pups at the same time. We read this AFTER we got our pups.
They are about 21 months now. It was a lot of work to have two puppies at once but we are glad now that we did. We don't see any of the problems that we were warned about.
I don't know if it is a good idea or not but it has worked out well for us.