All three degrees - MA(Hons) Economics, MA(Hons) Economics and Law and LLB(Hons) Law and Economics - are the same in first and second year. You have to take Economics 1A, Economics 2 and Issues in Global Economics.
Economics 1A and Economics 2 do make fairly heavy use of maths, particularly calculus. Lots of models involved - later years also feature probability (especially risk) and statistics quite heavily. The advice on DRPS (see thread about 1st/2nd year subjects) states: "A background in mathematics beyond GCSE level is recommended. Students with a weaker maths background will need to be prepared to work at developing their maths skills."
In Economics, 3rd year the core of the course is pretty quantitative (Econometrics) and you select a couple of topics to specialise in. 4th year only the dissertation is core and you get a wide choice of courses to take. Hence at that stage you can make the course as quantitative as you like.
Economics and Law, you do a bit less Economics in 3rd and 4th year (to make space for Law).
Law and Economics - you do a lot less Economics in 3rd year. You get no choice in 4th year beyond the 2 compulsory economics courses.
Only Law and Economics LLB (Hons) is considered a law degree. However, there is no guarantee it will be a professional qualifying degree. For professional qualifying degree in Scotland you have to take certain courses but on a combined degree you have less space to take those courses. The University state that if you have a clash with your other subject (e.g. if taking a 2nd year Law ordinary course in 3rd year and it clashes with a 3rd year Economics course), the law course is not available to you. See the Law School DPT page on DRPS for info.
Hence going down this route (wether you take Economics and Law or Law and Economics) will probably mean taking further legal training after you gradaute before you can qualify as a lawyer.
You can look up the courses on DRPS to find out more.
Economics and Law may get you onto an Economics MSc. Law and Economics very likely won't judging by Edinburgh's requirements for their Economics MSc.
BTW unless you explicitly hold an offer for Economics and Law/Law and Economics - don't assume you can switch to them. Law is a highly competitive course so there are limits to how many students they allow to take any Law courses as outside subjects. There is also a difference between doing the actual joint degree and just taking the subject as an outside course in 1st/2nd year.
BTW you wouldn't strictly need a quantitative subject to go into chartered accountancy or even Actuarial Science. Most big grad schemes just ask for any 2.1 degree. Some of the actuarial schemes only require a slight higher UCAS points total than straight accountancy/audit/tax.