It's developmentally normal and they do grow out of them. Worrying that toddler tantrums are an early sign of later delinquency is an outdated fear, worry not! :)
Don't allow a tantrum to change your boundary - e.g. if you were in the supermarket and say no to sweets, don't give in, if you offered them a choice between two yoghurts and they want both, don't take both away, either choose for them or let them calm down, then choose. If you were trying to give them a drink, don't take it away - they are still thirsty.
Some people prefer to ignore tantrums and some prefer to empathise. Both are appropriate. Neither gets them gone quicker, although I'm sure you'll find people swearing that their method works best. (It probably does for them - you need to find what works for you.)
Don't punish tantrums although it may be helpful/necessary to remove a child to a neutral location, take them out of the situation, take them somwhere safe, remove items that are becoming a hazard.
Don't try to reason/explain/chastise during a tantrum as they are not in a space where they can engage with you. If you want to talk about behaviour, do it after they have calmed down.
Mocking the child/joining in with the tantrum is a little bit mean and might be confusing for them, I probably wouldn't do that. Really though it just sounds like your DH is using it as a form of distraction. Sometimes you can distract them out of a tantrum if you're quick enough. Whether it's helpful...? Some parenting styles say fine, others say no as it's counterproductive/disrespectful to the child.
It's definitely normal for their age, but also your toddler is going through a huge upheaval with the change in the family and having recently been away from you - possibly for the first time ever? So a little extra leeway, kindness and understanding is really helpful. Try to keep as much as possible predictable and familiar - their whole world has just been rocked - talk to them about what will be happening next, and keep as much as possible low pressure and low expectation. If you have a visitor for example, it's a good idea not to do much if anything else that day. Make sure there is some one to one time happening with both you and your husband. Let as much drop as you can.
Useful books I'd recommend (probably not all of them at once 
)
How to talk so (little) kids can listen
Siblings without rivalry
The second baby book
The whole brain child
Big little feelings is meant to be good on instagram too and the book you wish your parents had read :)