Descent from Robert de Montgomery to Margaret de Montgomery (Line 222)

Robert de Montgomery (de Mundegumbri), 1st of Eaglesham, d. c. 1171 (A, C) or after 1171 (B); married Marjory FitzAlan (daughter of Walter FitzAlan, 1st High Steward) (A). 
Crawfurd & Robertson makes no mention of such a marriage under Montgomery or under Stewart while The Scots Peerage only suggests he may have married a daughter of the High Steward but makes no mention of any daughters under Kings of Scotland.

1

Sir Alan de Montgomery, 2nd of Eaglesham, d. 1190 (A). 
The Scots Peerage agrees that Sir Alan was Robert’s eldest son but says he was alive in 1202 and 1221. Crawfurd & Robertson skips this generation.

2

Sir John de Montgomery of Eastwood, 4th of Eaglesham, a. 1239 (B); m. Helen Kent (daughter of Robert de Kent of Innerwick) (A, B, C). 
The Scots Peerage agrees that Sir Alan had 4 sons (Robert, John, Henry and Alan) and that the eldest son (Robert) died without issue and that the second son (John) married Helen Kent, but does not identify this second son with the Sir John Montgomerie of Eastwood who The Scots Peerage says succeeded Sir Robert. Crawfurd & Robertson says that Robert was succeeded by his supposed son John de Mundegumbri

3

Sir Alan de Montgomery of Eaglesham, a. in 1208 and in 1232 (C), d. 1237 (A)
The Scots Peerage makes no mention of Sir Alan and only refers to a possible son called Alan who may have been a grandson

4

Sir John de Montgomery of Eaglesham, d. c. 1285 (A), d. 1285 (C); m. Margaret Murray (daughter of William Murray, Baron Bothwell) (A)
Crawfurd & Robertson agrees that Sir John was the second son of Sir Alan and that he succeeded the eldest son (Robert) when the latter died without issue. The Scots Peerage makes no mention of Sir John.

5

Margaret de Montgomery m. Sir Archibald Mure of Rowallan (A, B).
Crawfurd & Robertson makes no mention of Margaret but names the same four brothers (John, Murthaw, Thomas and Allan of Stair) that Barnes-Graham names (Sir John de Montgomery of Eaglesham, Murthaw de Montgomery, Alan de Montgomery of Stair and Cassilis, and Thomas de Montgomery).
Interestingly The Scots Peerage refers to the same 5 children (John, Margaret, Murtauch, Thomas and Alan) but identifies them as children of Sir John Montgomerie of Eastwood (generation 2); in other words 2 generations have been left out. Furthermore, The Scots Peerage only definitely identifies John and Margaret as Sir John’s children, expresses doubts about the other two and even suggests that Alan is a grandson. The Scots Peerage identifies Alan Montgomery of Stair as belonging to the next generation.