How long as HE been living in THIS house with you?
It sounds like he won't meet the test of for living in the home as his principal residence for at least 2 of the five years immediately preceding the date of the sale. Assuming that's the case and that they file a joint return they will still be eligible for a partial gain exclusion. The applicable regulation specifically addresses this:
(3) Special rules for joint returns—(i) In general. A husband and wife who make a joint return for the year of the sale or exchange of a principal residence may exclude up to $500,000 of gain if—
(A) Either spouse meets the 2–year ownership requirements of § 1.121–1(a) and (c);
(B) Both spouses meet the 2–year use requirements of § 1.121–1(a) and (c); and
(C) Neither spouse excluded gain from a prior sale or exchange of property under section 121 within the last 2 years (as determined under paragraph (b) of this section).
(ii) Other joint returns. For taxpayers filing jointly, if either spouse fails to meet the requirements of paragraph (a)(3)(i) of this section, the maximum limitation amount to be claimed by the couple is the sum of each spouse's limitation amount determined on a separate basis as if they had not been married. For this purpose, each spouse is treated as owning the property during the period that either spouse owned the property.
Treas. Reg. § 1.121-2(a)(3)(i) & (ii).