1. Son-in-law. This is a compound word, three separate words becoming a singular noun, so it needs hyphenated. Also, you are overusing the word real. It is not necessary for either instance. "...was giving her a hard time...". For the second instance, you could say "...she gave him quite the tongue-lashing."
As for "...tongue-lashing/She really gave it to him tomorrow.", I don't understand the use of the /. You should remove it. Also, you cannot give in past-tense (gave) something tomorrow as tomorrow means the next day. I am going to assume you meant yesterday, as in the day before. You could easily write this as "...she gave him quite the tongue-lashing yesterday."
2. It does sound odd, as it is a rather old way of speaking. If you are looking for a more natural, modern way to say this sentence, I would suggest something like "I'd love for you to come." or "It'd be great if you came."
Again, you have a very old way of speaking here. "Want some coffee?" or "Do you want some coffee?" and "Yes, I'd love some." Try to use conjunctions as much as possible when you are looking for natural speech in dialogue. Native English speakers use conjunctions as easily as we breathe.
3. As an avid gamer, I'd like to point out we curse a lot more than we should, but avoiding curse words here, I would suggest you drop really altogether. Really is an adverb that we don't use as often as most people think. Try to use interjections if you want to sound more natural. "Oh, you are really going to get it now. You're going to lose badly this time." or "Ah, you are going to get it now! I swear you are going to lose this time."
Something I want to point out here is that we don't need adverbs to emphasize a sentence. While we do use them a lot, it is suggested in writing that we avoid them.
4. "...self-interested and mouthy" might be a better way to say this sentence.
I hope this helps you out.