Hi, I have been looking at the Scotlandspeople website and because of the way the records are prior to 1855, its hard to make a determination on which if any cert corresponds to the people you seek. The few bits I found that are definites ( some you may have)...........
James Tweedle & Ann Todd married 28 July 1833
children of James & Ann:
Agnes Tweedale born 4 March 1834
Janet Tweedale born 5 June 1836
It appears that Ann Todd Tweedale died between 1836-1841 as she is not in the 1841 census and her mom Agnes is head of house living with Ann's husband James & the 2 daughters. Cannot find her death cert. There is the death on 25 January 1838 of a female Tweedale who is buried in Lesmahagow cemetery (which is where husband James was from-according to census) but no identifying info to say yes this is her. May be worth finding the cemetery records to see if perhaps?

In the 1851 census, Agnes Todd is still living with James Tweedale & daughter Janet. Agnes has probably married. There are 7 marriages of Agnes Tweedale(& spelling variants) between 1841-1851, 2 in Renfrew.
As to Agnes' husband John Todd, it appears he died between 1817-1841. The only thing is I could find no death in Renfrew for him. There are 4 in county Ayr and these in Glasgow/Lanark.......
Death: John Todd
17 Nov 1818 Glasgow
7 March 1827 Blantyre, Lanark
28 April 1828 Glasgow
30 Jan 1833 Glasgow
17 Aug 1837 Glasgow
1 Oct 1837 Airdrie, Lanark
5 May 1839 Glasgow
26 Sept 1839 Glasgow
29 March 1840 Glasgow
you would have to go through these to see if any may have info that would match with what you know. I also tried looking for the deaths of Agnes Strang's parents and again there are several so you'd have to look to possible narrow it down.
I could find no birth for Agnes Strang. As to John Todd, between 1765-1785 there are 10 births-3 in Ayr, 3 in Glasgow city, & 4 in county Lanark.
I just found on findagrave some listings for the Lesmahagow Old Parish Churchyard and I think this is where you should definitely look. There are quite a few Tweedle/Tweedale/Twaddles buried there from the 1700-1800's. Maybe Ann Todd Tweedale is indeed here. Hope this helps, Kim