What to do with my disabled mother-in-law after my husband passed away?

I am so sorry for the loss of your husband. Your children have lost their father and your MIL her son. His sudden death must have come as a terrible shock.
Call your local Area Agency on Aging and ask for their help. Is your MIL on Medicaid? Are their other family members who can help MIL or you? How old is MIL? Let us know what you find out. Hopefully others will have additional suggestions. My condolences on your lost. 

My condolences on the death of your husband.

If you would like to place your MIL in a skilled nursing facility take a tour of a couple of places and decide which one you think will suit her needs best. Once you've decided you can avail yourself of the services of their social worker who will help you do what you need to do to get your MIL in. Usually a person has to go on Medicaid in order to afford a nursing home. The social worker will be a great help in navigating the Medicaid system.

Deepest sympathy for all of you. Such a difficult position to be in.

Is your MIL aware? Have you spoken to her about the new situation? Would it work if she was allocated 24/7 care? Or do you need for her to move?

As 97yroldmom says. Call your local Area Agency on Ageing and ask for their help.
You need help. No shame is asking for it.

Good Luck

I am guessing MIL is in her 60's? Does she need nursing home care or would assisted living be able to provide the care she needs. She must be receiving ssdi. Medicaid would pay for nursing home care of she has less than 2k in assets. Call your county social services to see what assistance they may be able to offer.

Are there other children. If so, maybe a family meeting? Explain that you r not capable to take care of this woman. You have 3 children and I would guess if u aren't working you will need to eventually. Your children are ur priority. If no family then you may need to place her in a home. Suggestions are good.