The deployments of the 2nd Battalion, Royal Scots Fusiliers, from the archived website regiments.org.
1919.11 Black Sea
1921.11 India: Barrackpore
1931 China: Shanghai
1932.04 England: Catterickhttps://web.archive.org/web/20080112143 ... /021-2.htm
The birth in Malta is probably unrelated as it doesn't fit in with the above information. The information on Regiments.org is usually accurate, however, there could always be some discrepancies.
Do you know when Joseph joined the Army? Was he in the Army when he married Lilias in June 1909, or did he join during WW1? Even if he joined during WW1, with that prior service, he would probably have been looked on favourably to take his wife and family with him to India. Do you have any evidence that's wife remained behind in the UK, and did not travel to India with him? I think it very unlikely that in the 1920s he would have a relationship with an Indian, and I am a bit unclear why you think the child born in India has a different mother. I agree with the comments others have made that the references to slave owner should be ignored. This reference should not be in the transcript.
Joseph's service file would probably still be with the Ministry of Defence, but I believe there are some restrictions as to who can apply for it. However, if you were able to obtain a copy, there would probably be some details about the children he was claiming as dependents.