See an attorney before you sign anything!
My view would be that this woman has loaned the company money. She deserves to get that back, with interest (say, 10% APR - see an accountant for how much to pay).
All financial records belong to the band, with every member having full visibility.
Payback should be from all income sources until the loan has been paid off. Once the loans are paid off, she is entitled to nothing.
If she makes a booking for the band, she's acting as the booking manager, and should get 10-15% of the booking fee. The rest should be split between the band members.
If she wants to be a manager, she should get 10% of all your earnings - but should NOT get her money on the loans repaid - that should be accepted as her investment in the band.
She did not write any songs, so she gets no royalties. If her son wants to give her a proportion of his royalties, that's up to him. So if you both write a song, it would be 50/50. If she gets a cut, it would be (say) 50/25/25 - you still get your 50%. If you write a song without anyone else, she gets exactly 0%, and you get 100%.
Keep a tight hold on *your* song-writing royalties! Never give them away to anyone!
This all reminds me of the 1950's, when all the great musicians knew nothing about business. They all died poor, and their managers made millions. Knowledge is power!
Final thought. If your band is doing well enough that the above is a real financial issue, then you don't need her anyway....