I think do whatever you want OP, it's hardly a crime and no one will tell the difference between your baby and one raised on organically grown, hand picked, boiled with spring water purées.
Having said that, I am a bit bemused as to simply why you thinknots so much effort to steam a head of broccoli and purée it with a stick bender. I know you're busy with twins and feel you have no time. But genuinely, in the time it's taken you to write the posts on here, notwithstanding reading the replies, you could have made up a whole batch of stuff. Honestly.
I may be talking out of my bottom here but am I right in imagining that if MIL does a lot of cooking that you're not that confident in the kitchen? In which case I can see how it must seem like a mammoth task. But I'd suggest you tried it, just a couple of times, if it takes too long, fine, you've tried. But it'd take you 30 seconds to peel a carrot, another 30 seconds to chop it, pop it in a pan to steam with a splash of boiling water and unsalted butter if you like, leave it on the hob while you play/ feed the babies their breakfast/ have a coffee or whatever, then whizz it for 10 seconds at the end. Done. Or peel and chop and apple, tiny splash of water, into a bowl with a lid on, microwave for 1 min, mash. This will take less time than your baby porridge!
As I said, do whatever you find best, I blw only because I found if easier for me, if i'd found purées easier you can bet I'd have done them as I like whatever requires the least effort on my part ;) The only thing I would suggest though is to drop the other baby stuff like a hot potato eg the baby porridge... So full of sugar! Get the plain porridge oat sachets, one sachet will be a great amount between 2 babies. otherwise I really do think you're setting yourself up for a bit of a problem in the future as they'll be so used to sugary tastes.