Mothers small estate - questions

Location: Massachusetts

Not sure if this is the right place for this, if there is a better sub you know of I’d appreciate the recommendation!

My mother passed away last month. She didn’t have much, a bank account <10k. No credit cards, no car, no house. Some second hand furniture we sold on FB marketplace for less than $100 and clothes etc we donated.

Due to the small estate I am going to file a Small Estate Closing Statement with MA, but there are 2 things I am unsure about:

1. I received a letter from her late husband’s pension she was receiving. It was made out to “the family of “Mother’s Name””. It states that they overpaid her ~$600 for the days after she passed. They asked me to write a personal check to them to refund it(lol). Can I ignore this because we are not doing full probate? I understand that I don’t need to pay it personally but does it need to come out of her bank account before distributing it to her 3 children?

2. It is my understanding she has not filed taxes in ~10 years. I know there is a form I can complete to get this settled with the IRS, but does any refund go to her estate? Do I need that all cleared so I know how much it is before I can do the Small Estate Closure (ie if she is owed more than $15k it might go over the $25k limit for small estates). Or is this a case where the refund would go to her heirs directly? There is almost certainly a refund as she worked low paying jobs and had taxes withheld from her paychecks all those years. Probably <$30k a year in income.

Thanks in advance! Let me know if any additional information is needed.