Re: watery mouth, I find that some recover and some don't. I used to give daily Pen & Strep for up to a week if needed. I never forced a watery mouth lamb to drink, nor tubed them, as I found it didn't help. Usually they don't want anything for 24-36 hours when they first get watery mouth, then, if they're going to recover, start to look brighter, walk about and shout for milk. Some look so bright I put them straight onto milk, some I would give 12-24 hours Rehydion then onto milk. Always very small meals when starting them back onto eating - 150ml max per meal, not more often than every 3-4 hours, probably not more than about 600ml in 24 hours for the first 24 hours.
Some years you get no watery mouth and others you get a lot; the difference seems to me to be how long the ewes and lambs are indoors and the ability to keep the pens clean. Strong lambs get it as well as weaker ones, lambs who've had plenty of colostrum within the first two hours of life get it, one lamb in a pair of twins will get it and its sibling won't. Non-medicinal avoidance is to reduce the number of ewes and lambs indoors, reduce the time they spend indoors, thoroughly clean out between occupants, minimise seepage from pen to pen, put lime on earth-floored pens between occupants or disinfect cement-floors, do not ring males earlier than 24-36 hours. In our situation, with commercial flocks in the hundreds, we find it best to also use the medicinal preventative of a squirt of Orojet into every newborn indoors lamb as soon as possible after birth - minutes if you can, certainly within the first hour. And Oroject any weak newborns being brought in from outside, too.
And of course, make sure every lamb gets a good bellyful of colostrum or colostrum replacer within its first few hours.
So much for watery mouth. Coughs, colds and snuffles are another thing. Sounds like you are doing all you can - were the ewes on Covexin or Heptavac, and did they have a booster a few weeks before lambing?
Flopbot which rights itself is, I think, a lamb which is really a little bit premature. Floppiness which does not right itself, and usually gets worse as the lamb gets older and heavier, is, I think, more about mineral deficiencies. Selenium and copper are the two main ones for skeletal development, I think. Did your ewes get a good mineral drench mid-pregnancy? And, depending on their breed, copper capsules, injections or chelated drench?
As with most lambing problems, prevention is so much better than cure. So, as well as saving those lambs that you can, try to understand where the problems arose and work out how to change your management practices in future to avoid the same problems later on and in subsequent lambings.