Before I would make an educated guess as to whether or not any of the suggested suspects were involved, I would want to see the actual case file and in particular the ballistic report.
Remember that these murders went un-noticed until quite a bit of time passed. Because of that, any eyewitness statement of what they saw or heard - and when becomes suspect. Most people can't remember if something took place yesterday or the day before - let alone several days or weeks in the past. This also makes it very difficult for someone like Scolaro (or anyone testifying about him) to say where he was or what he had done weeks or even years before at a specific time.
I tend to agree that Scolaro does not seem like someone who would murder an entire family at the far end of the state - and still make it home in time for the Johnny Carson show.
The actual deed of killing the family is much more along the line of what Collins was actually doing before and after in other places in Michigan. And it also seems to fit what Edwards is known to have done. But trying to connect either of them with that family in that remote cabin is something else.
When it comes to firearms and ballistics - all I have seen is second hand statements of bullets or casings being like this or that weapon. If there was a solid, ballistic match with any other bullets/casings used in other crimes, or to specific recovered firearms - then the police should have stated the facts clearly. They did not.
The killer's choice of firearms was odd. A .22 rifle or a .22 pistol, or .25 pistol can certainly kill someone - but they are very under powered compared to just about any other choice. And yes, the killer likely DID run out of ammunition. He would have had to shoot each victim multiple times to kill them. A person with a .25, two inch barrel, automatic pistol would have a hard time even hitting his target at anything but point blank aim.
The idea of someone like Scolaro giving his firearms to someone else to use on the family is beyond strange. If a hitman has to use your personal weapon, you'd have to wonder how much of a professional he is - and what his angle is. It would be a perfect set-up for blackmail.
Ballistics is a science which can identify the type of rifle or pistol which fired a given bullet or its spent shell casing. Police could state with a degree of certainty what the make and model of firearm it was and sometimes they release this information to press early on. If at some point, a suspected weapon is found, it can be test fired and the bullet and casing compared to the ones in evidence for an exact match.
This, however, might be difficult if years have gone by before the subject firearm is tested because wear, rust, changing of parts, etc. might have taken place, changing the marks made on the bullet and casing.
Here is a link I posted on another thread recently regarding the subject of ballistic comparisons in regard to .22 casings and the marks left on them:
https://scholarlycommons.law.northwestern.edu/cgi/viewcontent.cgi?article=5241&context=jclc