If someone is an avel because his father was nifter (L”A) and then his brother is nifter (L”A), so he is within now the year of his father, however it’s still the shloshim of his brother…His hair is very long, may he cut it?
If a relative dies within the shloshim of another relative, this is known as aveilus techufah, and the halachos of haircuts are more lenient: It is permitted to shorten the hair somewhat, without taking a full haircut. This should be done with a shinuy (not in the normal manner).
The same will apply if a relative dies after during the year of aveilus, at a time when the aveil’s hair has grown to the extent that he has received a “ge’ara,” and it permitted to cut his hair.
If no ge’ara was received, but the hair was very long and fitting for a haircut (e.g. three months without a haircut), and then a relative dies, there might still be room to be lenient in shortening hair as above – though this is not implied by poskim in general.
For sources please see Divrei Sofrim, Chap. 40, no. 27, and footnote;