Brake force only weak, loud squeaking, rim gets hot

Hello. I have a big problem with my Twingo ( CO6, Built 95, 1.2, 40kw ). My cousin, who is well acquainted with cars, recently renewed my brake pads and brake discs. Now I have quite a problem with the brakes, which means I no longer dare to ride with my car…. So, the symptoms are: – poor braking performance – brake pedal gets hard while driving, and braking hardly possible – brake pads seem to rub permanently on the disc (can’t anymore really accelerate this and when I go down from the gas quickly drops off ) – loud squeaking / whistle – rim gets super hot – touch already after a short ride no more possible ( right side ,ehr than left ) – after the ride bad smell in the bike area My cousin has tested the vacuum, was also so far i.o…. but now he doesn’t know any more . Can it be the brake power amplifier ? And if, how can I check this ? Or what else can it be, and What can I do? I’m completely perplexed and don’t know anyone who can help me anymore… and I’m missing the money for the workshop right now. Would you like to give me tips!