It's a difficult one.
As others have said above, DLA is not paid for the purposes of rent. It's to cover additional disability related living costs, such as mobility and careers. If they get HB as well, then that will be how they pay their rent.
Unfortunately, as others have said above, mortgage companies don't like tenants on benefits. Not so sure about insurance companies. If you've inherited the property though you may be mortgage free which could mean it's less of an issue.
Do they have the option of a guarantor? That might be a mutually acceptable solution here.
As horrible as this is going to sound - when I was a landlord, I had a "no benefits" rule. The letting agents I used had this for pretty much all of their landlords i believe.
I think when Universal Credit comes they will be doing away with direct payments to landlords. The full sum for all benefits will go to the claimants, who then will pay their rent to their landlords out of it. And that, for me, is part of the problem.
It comes down to basic affordability criteria. My letting agents only approved tenants whose income exceeded rent by 3:1 (or something like that). This figure wasn't plucked out of thin air. It's based on whether you can realistically afford your rent and other living costs. If you have a benefits claiming tenant, and their benefits are paid directly to them, and 50% of their total benefits is actually their HB (or equivalent), then they are going to struggle to cover everything. It's actually pretty hard to evict non rent paying tenants - takes ages - so there's a real risk that if other competing priorities are given priority by your tenants (kids need new school uniforms, unexpectedly large gas bill, whatever) they may start paying rent late and expect you to just lump it.
It's high risk therefore imo. I know that will upset some people, but I'm not saying it to be mean.