To legalize a curb cut in NYC, your first step is to hire a licensed architect or engineer.

So, your property must be secured with deterrents to hopefully stop this from happening - but, it's impossible to guarantee security.

It couldn't hurt to call a couple attorneys right away to see what they say in terms of cost and suggestions for dealing with this quickly.In terms of mitigating any legal issues with your tenant be sure you are documenting every conversation you have had with the HOA in terms of asking them to make the necessary repairs.

A legal duplex will have everything separate.  

Maybe they've been burned by landlords in the past and are being very careful.You can legally reject them based on personality, facial tattoos, body odor, or other factors, but you better make sure you can prove that it wasn't based on any protected class like race, religion, familial status, etc.

Quote from @Michael Smythe: @Sean Gallagher legally you are correct, but many tenants do NOT know this.We take over properties all the time and close 80% of existing tenants sign a lease with us.True! 

Also, keep in mind that if you do self manage, you do put yourself at more risk for a legal issues.

If a guest stays for one week in July, the owner can't legally rent to another guest until August and must leave their unit vacant for three weeks.

That said, tenants sometimes push for alternative solutions, as in your case.Here’s what I’d suggest:Broaden Your Marketing ApproachFebruary and March can be slow months for leasing in family-oriented communities, but it’s not impossible.

Quote from @Chris Morris: Wholesalers in Detroit are making it nearly impossible to find good deals.