:welcome: to iBoats
Indy boater14
I have been in your shoes . . . young family looking to get them into boating. I started with a 22 ft sailboat, then after a few years the family found that kind of b-o-r-i-n-g . . .
Sine you are looking at 16-20 year old boats, condition, as stated, is going to be a big (big) factor. However, I would not ignore brand reputation, because a mediocre boat does not get better with age.
Make sure the cuddy cabin has restroom facilities (porta-pottie or even a pump-out head) . . . very important feature for family boating.
As far as engines and reliability . . . well there may not be much in terms of reliability, at least by comparative standards, such as automobiles. There is just something about engines when they are not used for 6 months things that were working all of a sudden stop working. Your FIL can probably tell a few stories in that regard. Anyway fear not, there are some decent engines and propulsion packages.
Since you will be getting an older cuddy cabin, you will most likely be looking at I/O (aka sterndrive) engines. Mercruiser is the way to go IMO. OMC is OOB as mentioned, but you will find some boats up to the year 1999-2000 that have OMC engines. Four Winns is one example of a brand that used OMC. Just don't do it, not even if the seller is giving the boat away.
Volvo Penta and Mercruiser are the primary survivors of the I/O engine world. Mercruiser has survived (thrived) much better as far as volume and servicing and parts availability and price. Alpha is the general purpose outdrive from Mercruiser. They are good and well-proven outdrives, good up to 300 hp of engine. Above 300 hp is where Bravo comes in. I have only used the Bravo drives, as the boats that I have bought over the years had 7.4L (454) engines. The Bravo outdrive was introduced in 1988. They are pretty much bullet proof IMO, as is the 454/7.4L engine.
As a side note. The engines are all going to be made by GM (General Motors). Mercruiser and V-P buy them from GM and then add there brand of fuel, electrical, exhaust and cooling systems.
You will find both carbureted and EFI/MPI versions of these engines (4.3, 5.0, 5.7, 7.4, 8.1., 8.2) EFI or MPI work great until they don't then there is hell to pay to figure out what is wrong. Often the dealers cannot quite figure things out. It all depends on how good they are.
If you plan on doing your own maintenance, then you can save some $,$$$ and perhaps aggravation vs. relying on local boat mechanics.
As far as the boat itself, keep in mind that the 'skeleton' of many boats is made of wood. The skin of the hull may be fiberglass, but the structure behind it is wood in many cases, particularly when you are buying boats from the 1990's - early 2000's era. Many boat companies still use wood, although most have switched to rot-resistant wood.
Wood can deteriorate (rot) and when that happens the structure of the boat is compromised. so, you will need to learn to look 'behind the shine' (as I call it) and inspect the gust of the boat as well as what is in plain sight.
So, read up on the mentioned check lists and take along the FIL and any other experienced boaters when you go look at prospective boats. Nothing will be perfect, so you will have to use your best judgement on selecting manageable imperfections.
Of the boat brands that you listed, I would heavily favor Cobalt over the others, maybe Chaparral as a second choice.