What to do when Sprint goal can not be implemented as more than 1 complex Spikes should be performed

This endanger the Sprint goal initially spoken out by the PO. What is the right way to act here? Negociate the Sprint Goal?

The Scrum Guide says: "People personally commit to achieving the goals of the Scrum Team".

Wouldn't it therefore be better to renegotiate scope so the agreed Sprint Goal can be met, and commitments honored?

If you are a junior team member, planning should be clear about the goal, and the story should be small enough to complete and meet the goal, so that there will be no such problems in the late sprint.

Tests, not separately as a part of quality inspection at the last stage of sprint, or a stage, or a step

If there is a phenomenon that the final stage is a link, or a stage, or a step of quality inspection, you are an internal small waterfall, which violates the scrum

Testing is what the team does as it completes each fearture

This endanger the Sprint goal initially spoken out by the PO. 

Can't skip this.  Why is the PO telling the team what the Sprint Goal is instead of the team deciding on the goal together? 

As to the actual question you asked it seems to me that this is an opportunity for the team to discuss their refinement activities. If you start on a story and then determine that you need to do further discovery in order to accomplish it, then your refinement may need some further focus.  For the current Sprint, I'd make sure this is discussed openly and frequently with the entire Scrum Team and every effort possible is made to accomplish the Sprint Goal or as much of it as can be satisfied. Adapt as the team goes based on the learnings.  You may miss the Sprint Goal but you will also learn a lot that can be used for future work and activities. 

Failures only exist when you don't learn from difficulties.  Missing a Sprint Goal is not catastrophic but make sure that the entire Scrum Team learns from the exercise. 

To echo Daniel's comments, a spike is simply a formalized, focused refinement effort intended to learn and improve the likelihood of completing future related items.   Therefore, I see a couple questions that the Scrum Team may want to discuss:

 

1. Why did the Development Team agree to a forecast and Sprint Goal if refinement wasn't complete (multiple spikes in sprint)?
2. Seeing as there are junior members on the Development Team, is it perhaps prudent for the Development Team to slow down and aim for smaller Sprint Goals?