My 5 yo son has been potty trained for 2 yrs. since i started potty training my 3yo son, the 5 yo has started having bm and pee accidents. attention?

Definitely: Christina, as a parent and a doctor, I can tell you this is very likely. It is common for older children to regress when their younger sibs are getting atention. Just be patient and let the older one know you still love them and that they don't need to vie for attention. Hope this helps!

Sounds like it: Sounds like an attention grabber, since mom is spending time with the 2 yo, and all the attention is on potty training, etc. Try and have an activity with the 5yo and when training the 2 you say things like your smarter older brother learned this already and maybe he can show you how to do it, etc. get him involved and praise him for his efforts. Good luck!