Kev is a good friend of Fiona's, and knows fully well that the Gallaghers need the money that Frank spends shamelessly at his bar—and he sitll lets Frank do it? And the Gallaghers are okay that their closest freinds are basically enabling their father's drunken lifestyle?
I recall many times where Frank doesn't pay his bills and where Kevin reminds him that Frank still owes money. Kevin probably lets him slide a lot knowing the above. Also Kevin can't actually keep Frank from spending his money on booze, and if Kevin refused to serve him Frank would just go somewhere else for it anyway. Somewhere where they may not be as forgiving if he skips out on paying or acts too raucously. I look at it this way: Kev is babysitting Frank and keeping him from getting in deeper shit.
Why did Norma live in the Gallagher's front garden for more than a couple of nights? She had her own house for God's sake.
It's already been covered in the WMG section but we need it for completion: Joey and Donny Maguire. That is all.
The Maguires are established as a local "hard" family on the estate in early seasons. They're drug dealers who run the estate and it's easy to see why. Paddy Maguire is a psycho who beats people who owe him money down in the streets while laughing like a lunatic, Mimi is a cold-blooded Fat Bastard who threatens to cut people's bollocks off with a kitchen knife and headbutts anyone who pisses her off in minor ways, there are 3-4 (later revealed to be 6) brothers and the mates of the brothers as enforcers, and said brothers go around with fierce dogs at hand. In the later seasons, we're led to believe that they grow in influence to basically become something like The Sopranos but more scouse/Irish/Mancunian, yet it's puzzling why: First, they move out of their semi-fortified house with a hatch on the door and a torture den in the basement to a normal run-of-the-mill council house. Second, the Mooks stop hanging around. Third, the brothers start leaving. Towards the later seasons it's basically only Mimi with Jamie and Shane left. How can they control not just the estate but the large 'patches' they have in this situation?
Season 1, Episode 10 (the American series): Bob's scheme to take Liam away by proving Liam's true ancestry was doomed to failure, no matter the results of the DNA test. Illinois is a "presumptive paternity" state (like 47 other states), meaning if a woman has a baby while she's married, her husband is the father, regardless of whether or not he actually sired the child. While this particular law is intended to serve a different purpose (ensuring a divorced father remains obligated to care for children he'd previously accepted), it would also preserve Frank's parental rights if it had turned out Liam truly was some other dude's biological son. That's not to say a family court wouldn't have sided with Bob and Monica anyway, but the DNA test would not have empowered them to bypass the court battle the way Bob was convinced it would.