Bathing baby twins is no different than singletons except you have to do everything twice.
Bathing baby twins at the same time is not practical or even safe. You are better off bathing them separately one after the other. It would be very helpful to wait until you have help in the house to bath your babies.
Never ever leave your babies or toddlers in the bath tub unattended. Some people use their kitchen sink to bath their babies, but baby bath tubs are very practical and useful.
For potty training you can start at anytime you feel your toddlers are ready. However, it may be easier to wait until they are about 2 – 2.5.
(one of my twins wanted to use the potty right after her second birthday and she was fully trained in two weeks. The other twins showed no interested for another 3 months).
The plus side of training them earlier though is cutting on the cost of diapers.
If you plan to travel with your toddlers or even go out to the grandma’s, you may want to consider a travel Potty.