Can a non-POA family member sue the estate for 20+ mos of live-in caregiving services?

I can not get sibs (3) to agree to meager compensation I first asked about over a yr and a half ago (then $200/wk for live-in caregiving except for an outside 40-hr/wk job). I left a job in another state on a FMLA 5 yrs ago to help my mother. After numerous failed attempts at reasoning with them (and countless hurt feelings), a cost benefit anaylsis of the savings my presence/sacrifice has been to Mom, I can not get them to agree to meet with a mediator because they've continually dismissed my requests to greed. Very recently they agreed to paying me under the table (to avoid taxes) but no retroactivity. I explained that that would be fraud. They have since pulled that off the table.

And most recently they agreed to try, for the first time in over a yr and a half, to chip in and help out with Mom in 4 hr shifts M-F, 5 - 9 pm so I can have some time off after my 9-5 outside job, and some coverage on Sundays. Saturday coverage is still mine bc no one wants to give up their Saturdays. It's about 40+ hrs that they've agreed to help cover. This attempt started on December 15th. I am covering almost half of those 40+ hrs as well as overnight coverage. It's been tense and awkward, but they are trying, right?!

My question is, since I have gotten NO WHERE in trying to reason with them, it was mentioned earlier, elsewhere on this website that one could sue the estate upon her passing. Is that even possible? Is it possible without a caregiver agreement in place (they've refused that idea completely for various nonsensical reasons)? This would be my LAST resort, but might alleviate some of my stress and help me maintain focus while she's still with us.