It really grinds my gears that people cannot differentiate between "care" and "help". Most people happy to HELP with things like organising online shopping and making sure bills are paid. Or popping in for a chat and a cup of tea. CARE is a whole other ball game and no child or grandchild should be reasonably expected to shower or toilet an elderly parent or grandparent.
Also, it's a choice you have made here @AonRudEile , whether you've made an active decision to step up as a carer, or more likely, have fallen into it over time by taking on a bit more each time. It's easily done and you have to get to crisis point before anything changes. That's pretty much where you are now. You can't force your brother to take on some of the load, and he doesn't have to do any caring if he doesn't want to. That's as equally valid a decision as choosing to care for your parents, there is no judgement here as everyone's situation is different and you shouldn't feel guilted into doing care for your parents at the expense of your marriage and kids.
Agree that it's time to ask social services in to do a formal needs assessment for your parents and ask what sort of care is available. Either carers to come in, cleaners, meal deliveries, or maybe day centres or similar.
It's OK to say you can't cope with this any more. You have not failed, it doesn't mean that you don't love your parents.
Take care, OP. It's not an easy path.