they got it or they had got

I think it should be "they had their garden decorated" but I'm not sure.

thank u for your answer ,but I mean the second part ?

they held the wedding ceremony at their house ....

they had got the garden decorated or
they had the garden decorated

I want to say that they action of decorating was before the wedding ...passive & past perfect

violetethey had the garden decorated

This one. This is a causative (passive) construction, The garden was decorated as they desired (perhaps by friends ir professionals).

By the way, if you care about grammar, you should care about capitalization, and please show a little regard to people who try to help you do not

violeteI want to say that they the action of decorating was before the wedding

They had had it decorated or They had got it decorated.
Some speakers would say had gotten. (AmE)

had had is the past perfect of have; had got is the past perfect of get.

Thanks everyone
But I did not know that it was not nice to use texting style ( I'm a learner)

Texting style is fine in informal texts and emails and in chatrooms. In this forum we ask people to do their best to write in a manner that can be used by learners at school and work.

We are, of course, also happy to answer questions about informal English.