Can we do a straight swap 98 Grand Am 2.4 out and 3.1 from 95 Chevy Monte Carlo in?

No. The mounts are different and the PCMs/wiring would need to be swaped. There may be other issues as well.

It's possible. You'd need the mounts and wiring from a Grand Am SE V6.

It's not a "straight swap" but it's doable without fabrication as long as you get the right parts.