I know I won’t always be there, but I hope B and M will have each other for life. So it’s not too early to teach them to help each other out. They can help each other pull off the sleeves of a particularly tight shirt, pull up the other person’s underwear (usually from behind where they can’t reach themselves), pull off each others’ boots, fetch things for each other, etc.
It’s cold here and M has a runny nose. Here’s a video of B helping M fetch a tissue to wipe her nose: