Can anyone give me any information regarding the large variety of covers addressed to this lady?

They bear a wide selection of censor marks: 6/5215 (scans attached), 6/2640 (hand note on the cover "Leopold"), 6/4783 (Bertie"), 5/4280 etc

Some, but not all, are signed by what I assume to be a member of the family, as per the scans. Sometimes he puts "RE" after his signature. Leopold Harris was a Captain in the Royal Engineers, but I'm not clear if this is his signature. The one with his name written on was signed off by someone else

Any ideas?

Here are two more covers, both bearing the franking of APO S40, dated two days apart in October 1918. They are both signed off by the same officer.

However, they bear two different censor stamps - 6/5732 and 6/6983. Was he signing envelopes delivered to him from different units? Does this suggest the signature is not connected to the individual unit stamps?