If the glass is tempered for strength, it cannot be cut without annealing it first. At that point, it may be cheaper to purchase a new top. Here is a link that might be useful: cutting tempered glass

I would call your local mirror and glass company. Sometimes the weight of the glass is all that keeps them in place (it would be shatterproof glass for safety). We have also used silicone iirc on outdoor tables. The bigger issue may be what the base looks like when you remove the top; if it was not designed to be on display it may need finishing, or may be too crude to look attractive.

https://www.fabglassandmirror.com/glass-table-tops?gclid=Cj0KCQjwjbveBRDVARIsAKxH7vl0qwo8M5IC__eD5mixBLk_K1mWYD33IASECIdKFnszcqoBdysIAJMaAqtmEALw_wcB Here's a source that should help you decide. They will answer all your questions. Have you considered a racetrack shape for a table which is that large?

I like the 4 tables they can be moved when you have a party and that space needs a large table so they work nicely > IMO the layout of the space is a bit odd since the seats facing the TV do not look comfy for TV watching but maybe the TV is not important to you.