Re: Your first question. If you are talking about giving someone a blessing in the hospital where you technically cannot touch them - you just do your best and the Lord will understand. 
 
Yes, and elder (or for that matter a priest in the Aaronic Priesthood) can do it by himself. However, he has to get permission from the Bishop before doing so. 
 
Here is a good place to learn more about priesthood guidelines and instructions: Link

In order for a Melchizedek Priesthood Holder to be able to bless someone he need to lay his hand upon there head. If he cannot make do so he can pray for them but not bless them.  
 
An Elder can preside over a meeting in the absence of a High Priest and administer the sacrament through his priesthood authority or by delegating that authority to an Holder of the Aaronic Priesthood in the office of Priest.  
 
This rarely happens though unless you are in a small or new branch.

If a melchizedek priesthood holder gets premission from the bishop to bless bread and water for himself and another member,but the other member doesnt show, can he still bless the bread and water for himself?

i just asked this but you didnt have my email- if a melchizedek priesthood holder has permission from the bishop to bless the bread and water, for him and another member but the other member doesnt show. can he still bless the sacrament for himself?