Question about entering UK

A friend of mine just married and got offered a job in London and he's coming with his wife in about a week, he's Italian and his wife is Argentinian, because of the short notice I believe there's no time to do a family permit so they're planning on coming and applying for pre-settled status from inside the UK, just in case they need it they had translated by an official translator her birth and marriage certificates.

Is there anything else they should do? Should they expect any problem when arriving? Do they need an apostille on the birth & marriage certificate or that's not necesary?

Thanks for the help!