[ksa]

составить регулярное выражения для выбора первых двух предложений из текста

Как вариант...

var txt='English singer, songwriter, guitarist, record producer, and actor... ';
txt+='He attended the Academy of Contemporary Music in Guildford as an undergraduate ';
txt+='from the age of 18 in 2009. In early 2011, Sheeran independently released ';
txt+='the extended play, No. 5 Collaborations Project. After signing with Asylum ';
txt+='Records, his debut album, +, was released in September 2011. It topped the ';
txt+='UK and Australian charts, reached number five in the US, and has since been ';
txt+='certified seven-times platinum in the UK. The album contains the single ';
txt+='"The A Team", which earned him the Ivor Novello Award for Best Song Musically ';
txt+='and Lyrically...';
alert(txt.match(/([^\.]+\.{1,3}\s?){1,2}/)[0]);