Ok this is going to sound alot weird: I am actually trying to help a BM.
Really long story made short: her XH cheated. Came home one day out of the blue, moved out and moved in with his 22 year old 'assistant'.

Old order:
XH made about 80k a year. Her CS order is from Michigan and was determined when she and her ex huband had 50/50 that he would pay her 1k/ month. Five years ago she moved to Florida. She has both children full time father sees them 2 weeks a year (his choice she has offered more time). While custody was modified in court, cs was never updated. She has been receiving the $1k per month for the last five years.

Michigan recently sent her a letter that her XH is seeking a cs modification and he has apparently been taunting her via phone and email that her payments are going to go down because the kids are older (teens) and dont cost as much to raise anymore??

Mom is disabled (in a wheel chair currently with MS and she is seriously impaired physically) was diagnosed at the time of divorce but not disabled(yes, XH left her two months after she was diagnosed with MS). I told my friend I do believe her payments will actually go up, not down and her xh is going to kick himself. I think that because the time split changed (legally) and she has the kids 96% of the time instead of 50 that he will likely be found liable for a higher cs amount.

Her question: Does she need to hire a lawyer for this to protect herself or will Mighigan cs people be able to handle it withouth lawyer interferance (she really cannot afford an attorney). And so she can budget/plan does anyone know how to do the calculations?

Mother annual income (diability $494.00 per month x 12= $5928.00)
According to the documents she got XH is stating that his annual income is $106k
Father is responsible for 90% of medical costs due to a refusal to cover the girls on his insurance policy (this is Co'd)