Is it true that if one drinks alcohol in someone's house, their prayers will not be accepted for forty days? And is it forbidden for me to allow my friends into my room if they have drunk alcohol in it? And how should I deal with them if they refuse to abstain from that?

You must avoid bad company that leads to evil and assists in it, and you must forbid drinkers of alcohol from their actions. Part of forbidding this evil is preventing them from drinking alcohol in your house. If they insist on drinking there, do not allow them entry, as an exoneration before Allah and a fleeing from sitting with them or appearing content with their actions. As for the prayer not being accepted for forty days for one whose house was used for drinking alcohol, there is no evidence for that, and the narration mentioned pertains specifically to the alcohol drinker himself.