The first 2 transactions are marked as 'Unconfirmed Parent' and the third transaction is marked as 'Unconfirmed'. What's the difference, do they link with each other ?
When electrum says that a transaction has unconfirmed parent, it means that the fund which is being tried to send in that transaction has been received in a transaction which is still unconfirmed.
Assume that you have sent bitcoin from address A to address B and then the same coin from address B to address C.
As long as the transaction made from address A to address B is unconfirmed, the transaction made from address B to address C can't be confirmed.
The two transactions that have been marked as "unconfirmed parent" can't be confirmed before confirmation of their parent.