Explaing Mortgage payments to seller for subject to deal

[Jade Reynolds]

I came across an off market property that owes 125k on loan, seller motivated, comps are $115k-$140k. It would not be a good wholesale deal seems like so I want to try a subject to deal for myself. I have never done this but pretty excited to try to get my 1st rental property with little to no money down. I think i understand the structure of it but not the execution. My questions are:

Will the seller ask his lender if this is legal/doable? 

Will that answer bring confusion and cause him to decline my offer?

If he accepts, how do I execute?

After closing do I pay mortgage payment directly to seller or mortgage company?

What do I write on the contract?