Yes a husband and wife can be buried together in the same casket if they die soon after each other.
For example there was a couple who were married for 77 years who died in 2017 and the couple died within hours of each other.
The couple who died hours apart and were buried in the same casket were Raymond and Velva Breuer.
They were laid to rest in the same casket that was made big enough for two people.
I guess it would be possible to dig up the other spouse that died and then lay the other person to rest in the same casket if you order a large enough casket.
But a standard casket would not hold 2 people so you would need a special made casket to bury two people in.
If one spouse dies and the other dies years later then you can be buried next to each other instead of in the same casket.