Advice for older couple

By shopping several Winnebago dealers, you just might be able to get the 22C or 22E, new, for around $55K:
https://winnebagoind.com/products/class-c/2019/outlook/floorplans

I don't think size generally correlates with extra problems, either as an advantage or a disadvantage, generally speaking. As to whether it would be sufficient for you and some grandkids, that's really hard to say; it depends on the personalities involved, your expectations, the ages and general stature of the grandkids, and a host of other things. I would look for a decent size cabover bunk to minimize the effort in transitioning from daytime use to nighttime use and back (if you don't have to fold up a dinette table, that's a definite plus).

A corner bed can be hard to make and inconvenient to access, particularly with more than one person sleeping in it. If the person next to the wall needs to make a nighttime run to the bathroom or whatever it may well mean waking the other.

More important than age in my opinion is condition when buying a used motorhome. A well-cared-for 2011 can have lots of life left in it with (comparatively) minimal problems if you also take care of it. A two or three year old unit without proper care may be in worse shape.

For what reason are you particularly drawn to smaller units? Some reasons are very good (the spot where you store it is only so big), some are reasonable but very often overestimated in importance (you can find more campsites to fit smaller rigs), and some in my opinion just really not true (shorter units aren't really easier--or harder--to drive down the road, though of course maneuvering in tight quarters is a little easier with a smaller vehicle).

Your budget should be sufficient to find a quite nice unit indeed.

Size is very personal. Some people can travel full time in a 16' travel trailer full time and be very happy. Others need a 40' 5th wheel and still feel cramped.

Personally, I would want to get at least up into the 27-30' range. Particularly on a rainy day with the 3 grand kids...but as long as it's a short time, you can make it work in a smaller unit.

Lots of options in that price range. I wouldn't consider a unit without slides and for the most part they are reliable.

If you are new, find a mobile RV tech and pay him a couple hundred to go over the unit once you think you've found a winner. The single biggest issue with all RV's is water leaks. A good tech will be able to find evidence of prior leaks.

I have a 31 ft coach and I wouldn't want to even think about a 23 - 24 ft coach with 3 grand kids in there with me and my wife.... Even for a weekend. I don't think that you would regret the 28 ft coach at all. There are plenty of good used coaches in the size your looking for. Like another poster has said, the biggest killer of RV 's is water intrusion... Period. I know other RV owners that bought big and then went smaller and vice versa. Most say that it's easier to trade down then to trade up in size as far as trade in allowence is concerned. $$$

I have a 28 ft Class C and traveling with 3 kids would be a challenge. If they are old enough consider buying a suitable tent - they can sleep outside.

If you not in a hurry you can find a suitable used rig. My rig is ancient (92) by some peoples std but it's well maintained, everything works fine and it looks good. Not many like mine but there are some - just be patient.

Don’t be afraid of an older unit if it has been well maintained. I had a 2000 Hurricane 30q bought it in 2012 sold in in 2015. Just some minor engine maintenance issue and such. We bought what we have now with bunk beds to use for great nephew and a place for pet cages and supplies. 30 ft is a good size as has decent space, easy to maneuver. I think the shorter units are easier to get into small spaces but have a harsher ride due to the short wheel base, minimal storage, and you’ll want to trade up after a few rainy days with the five of you stuck inside.

Net of the above for your price range you can find a mid size C or A class that you will be happier with, but that’s my opinion.

I purchased a 2004 Winnebago 3 yrs. ago. It was well cared for and has given me no trouble. Have a knowledgeable friend check out any unit you are thinking of buying. As for size - 23 or 24 ft. unit is fine for two people, however, if you are thinking of taking your grandchildren along a lot you will be very crowded.
Remember a 24 ft. unit is measured from the front bumper, so there is not 24 ft. of living space.

Check out PPL Motor Homes .

Will the grandchildren always be with you? That might affect your decision. Some RVers take tents and blowup mattresses...

Consider how you will use the RV most and how often the grandkids will be joining you. For example, are you going to drive to the lake for the weekend, park it, and let the kids play outside? Or, are you taking the kids for the summer and crossing the country and seeing all of the national parks? (All will be inside for much of the travels.) Will the grandkids be with you only once in a while, or do you provide child support while the parents work? The answers to questions like these will help you focus on the kind of RV that works best for you.

We have a 27 foot RV, and our two adult daughters and sometimes our Son in Law travel with us. Often we take long trips, several have been cross country. Whether for the two of us, four or five of us, smaller than 27 feet would not work for us. Yes, you could make 24 feet work for you, but it will be real crowded with all of your grand kids (IMHO).

Good Luck with your search.