You might or might not be able to adjust the heels enough. Boot shells only come in full sizes; half sizes have different liners. If the prior owner was 25 and you are 26.5 (for example) there's a 1 cm difference and you probably have enough range to adjust, depending on where in the range the heel pieces were when they were mounted. I'm not finding the adjustment range on line but I think it's about 2cm, so if the binding was mounted with the heel centered in it's track it can go 1cm forward and 1 cm back. However, if his boots were 25.5 and yours are 27, that's a 2 cm difference and you are out of luck, unless the heel was all the way forward in it's track when it was mounted, which is unlikely. Even then, no need to sell the skis. The bindings can be remounted as long as the new holes are 1cm or more from the old holes and the old holes are properly plugged. One more set of holes will reduce the resale value but not the strength or performance of the skis. If drilling lots of holes through things weakened them too much my house would have come down around my ears years ago.
My sons and I are one shell size apart and we swap skis with both Griffons and Solly Z's and STH's--sometimes I have to max out the heel but I am always able to get the forward pressure correct.
You can try it yourself--the heel adjusts with the small screw at the back of the heel housing, which should stick out a bit when the boot is out of the binding. With the boot in the binding the end of the screw should be flush with the back of the housing if the forward pressure is correct. If the binding is mounted too small for you you might be able to get the boot into the binding with the heel all the way back but the end of the screw will be recessed into the housing, in which case the binding won't release when it should. It's OK to play with this stuff on your own to see if the bindings will work, but based on your level of knowledge you'd best take them to a shop for accurate adjustment. (Note that when you put the boot into the binding on the bench, while you can do it by just pushing down on the boot, it's a lot easier if you close the heel by hand as you push the boot down.)
Those bindings and what little I can see of the ski look barely used.
Oh, and next time skip the respectfully part. It just gives us a swelled head.