Will this affect credit?
To me, this is a hair brained idea. It might solve an immediate problem, but I think it's a bad idea for several reasons.
Some relatives (1 & 2) are supposed to clean out an old house of another relative so the house/estate can be put up for sale. The problem is that another individual (3) who grew up in the house has his junk stored there and won't move it out because he has no place to put it. Relatives 1 and 2 want to get a storage unit, pay for one month, and tell Relative 3 to assume the payments or move the stuff elsewhere. In all liklihood, Relative 3 will default on the storage area even with his junk in it and the landlord of the unit will be forced to auction/throw away the junk.
My question is won't a default on the storage unit ding the credit of whoever secures it initially?