How to joining in Jama’ah? How to then complete the missed units?
You have secured your Jumua’h salaah if you joined the imaam before the salaam.
Hanafi – Waajib to pray with congregation
Hambali – Fard
Shafii – Sunnah
Congregation in Masjid is sunnat mu-akkada
Someone who does not pray his fard salaah in masjid when it is near one’s house, his prayer will be defective.
Imaam not having wudu invalidates entire congregations’s salaah.
It is not necessary to investigate whether the Imaam has done wudu or done properly. Dhunnu bi mu`mineena khairan.
However if one happens to know somehow that the Imaam does not have wudu. Or has done wudu by wiping over normal / cloth socks then one needs to repeat his salaah. This is because wiping over cloth socks is not considered a valid way of completing wudu according to all the classical madhhahib.