We sold our manufactured home as contract for deed 8 years ago. The buyers have been responsible for all payments including insurance and property taxes. Now they want to sell it. Can they do that without us being involved? Our name is the only name on a copy of the title from the DMV. How does a sale on something like this work?

Depends on what the contract says.
1. does it say they can sell it
2. does it say they can not sell it?

How do they plan on selling it, on a contract for deed also, or just to a buyer for cash.

But they sell it, and at closing you are there to sign the title over to the buyer.

I have bought on contract ( less money of mine out, and does not show up on credit report as outstanding debt) and then sold those houses after fixing them up a dozen times , most likely more. Also most buyers on contract seldom actually finish paying off a contract, they more often let it go back, but others sell it to someone else to get out of the debt.

At the sell ( closing) of the home, you will get your payment in full that is shown on the finance documents of your contract, and then you sign the title over.

Of course the entire issue is that a contract for DEED, would seem to say there is a deed, so is there also land selling with this, that has a deed? Or is it just a title of a home.

Since this would really be a personal property ( trailers are personal property since they have a title,) they are not real estate with a Deed. And would have been sold on a personal property installment contract. But the real issue is that it was done and written properly.

It depends on what they are selling. Depending on the wording in the contract, they may be able to sell the contract. If so, they may be able to do this without you being involved. The buyers would then be responsible for all terms of the contract. You will still own the home and you can still default the contract if they don't pay.

They can't sell the home since they don't own it.

Read the contract, everything should be spelled out in the contract.