can/could question and plural of words ending on a S

0 00Hello again,02br
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00Firstly, I would like to apologize for posting in the wrong forum category. As I'm not a native English speaker, all of my questions will probably be quite easy. 02br
00I'm really doubting about the following text fragment, which has led to some lengthy discussions with a friend of mine05000.02br
00Could someone please correct it and tell me why it is supposed to be this way? 02br
00I've marked the fragments I am in doubt about but if there are more mistakes, don't hesitate to point them out.02br
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00This was the sentence which kept lingering in my 01font00parents’ head(s)01span02span00 or parents's head(s) 02font00after their visit to the 01a01span00gynaecologist02span02a00. 01u01span02span02u01span02br
02span00After spending nine months in a sheltered place, my sister and I were finally born. N00ow01span01font00,02font00 02span00 00my parents would discover 01span00how having twins00 01font00can or could02font00 00change their lives. 02br
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00Many thanks,02br
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00Jeroen02br
02span00 010id1