I am travelling to DC with an elderly lady and a disabled guy though not wheel chair bound there will be 4 of us
Does any one know if its possible to have a private guided tour.?

I don;t think your need is for a private guided tour. Unless the guide is carrying the elderly lady and disabled guy that won;t help them negotiate the very long distances in DC.

I would consider renting a folding wheelchair for the disabled guy (my dad doesn;t use one ordinarily but does for long dstances - like large airports)and then simply get a cab from one place to another.

I think that would involve the least walking overall.

The other thing is to make sure you have a central hotel with a good taxi rank.

Ummm, I'm not an expert, but I haven't ever heard anything good about DC taxis - from what I hear they tend to be expensive and dishonest.

Was there somewhere specific you wanted to visit that you wanted a guide? Are you staying in a hotel?

Have been in DC cabs dozens and dozens of times and they are certainly not expensive (and the fares are controlled - they just don;t charge what they). Especially when you consider there are 3 people involved.

As for dishonest - I've never had a problem - but perhaps you're not familiar with their zone system.

I am pretty surprised about the DC Taxi comment... after years of traveling to DC I have always thought they are amongst the friendliest cab drivers in the US.
I have had many interesting conversations.
To me the most dishonest I have come across are to/from the airport in Vegas... extremely friendly but tricky. I have had several distract me with friendly conversation as they drove the long way. Now that I know Las Vegas a bit better I can see when they are trying to do this and let them know that I know the game... it happens often!