Laddy McDeath (50 kills with grenade launcher) goes by very quickly if you're even halfway decent with the pipes. You can also get points toward Glasgowned (25 Scouts/Pyros killed with pipes) during this grind, try to get Caber Toss (pipe someone in mid-air after you bounce them), and always look for chances to get Blind Fire (kill one measly sentry without being in its line of sight). Taunt when you blow someone up for your free Bloody Merry tauntchievement (or Second Eye if it's still bugged). This will get you .... the Targe, unfortunately. That's not going to help you much with getting more, since the damage seems bugged enough that The Targe Charge is basically impossible/sheer dumb luck right now. Luckily, all this blowin' up should have gotten you Well Plaid (10 Demo assists) with all the Demos currently running around.
But that's okay, pull out your sticky launcher. Get a giant fucking jump with Highland Fling, then sticky up the first unguarded teleporter exit you see for Loch Ness Bombster. Get some stickies on a cart to try and gib three idiots (quick, free weekend is almost over!) for Pipebagger (blow up three in one stickysplosion) and credit for Scotch Guard (do that three times, only counts on a cart). Try to kill all comers with mid-air activated stickies for that kill grind. All this blowing people up should hopefully also be including dead defenders and buildings, giving you credits toward those grinds toward 25 Dead Point Defenders and 50 Kersploded Buildings. Try launching players with one or two stickies to kill them with fall damage for He Who Celt It, and always look for an engy/sentry/dispenser combo you can safely take out with one sticky explosion for the Argyle Sap.
Popping enough of those (You're gonna need 10 achievements total, with Milestone 1 counting for your 11th) you can get the Eyelander and basically go to town on swordchievements until you get the Scottish Resistance. Actually farming achievements as Demo isn't easy outside of achievement servers, but there's plenty of low hanging fruit to keep trying for while focusing on a couple of the more accessible grinds.