The first two covers are from 1873, just before the inauguration of the General Postal Union in July 1875, so rates were determined by individual treaties. The top wrapper was charged 6d from Bristol to Stockholm in April 1873 - the large red 2½ mark would have been an accountancy charge. The second cover is from Bristol to Canada in September 1873 and is franked with a 3d stamp. From 6th January 1870 the postal rate was 3d postage paid, with a fine of 3d if posted unpaid (ie. charged 6d).
The Universal Postal Union began as the General Postal Union in July 1875, and took its current name in 1878, although rates could still vary between UPU and non-UPU destinations until 1892. The top cover to France sent in 1877 paid 2½d while the lower postcard to Cadiz in 1892 went at the 1d international postcard rate.