As Dick Harfield mentioned, the text does not provide or lead toward an answer through hermeneutics. By exploring your second question regarding "due penalty," however, there are some verses to consider in order to hopefully bring better clarity to what you are seeking.
"Due penalty" can very well refer to venereal diseases. On a deeper level as well as keeping consistent to what the verses around verse 27 state, the "due penalty" suggests to be tied to sin: the nature of sin and God's judgment toward sin.
In verses 24, 26, and 28 we read not once, but thrice, that God gives man up to sin.
"Therefore God also gave them up to uncleanness" -- vv. 24 (NKJV).
"For this reason God gave them up to vile passions" -- vv. 26 (NKJV).
" God gave them over to a debased mind, to do those things which are not fitting" -- vv. 28 (NKJV).
These verses are certainly noteworthy because they reveal sin as unrighteousness before a righteous God Who will judge / penalize sin. With this framework in mind, here are two sources that may help you better understand the "due penalty" that is subject to those who will receive (it) "in themselves."
@EnduringWord Bible Commentary
e. Receiving in themselves the penalty of their error which was due:
Paul speaks of a penalty for homosexual conduct; homosexuality has
within itself a penalty. This speaks of the generally self-destructive
nature of sin; it often carries within itself it’s own penalty.
i. Sometimes it is the penalty of disease, which is the consequence of
violating nature’s order. Sometimes it is the penalty of rebellion,
resulting in spiritual emptiness and all it’s ramifications. In this
sense the term “gay” is wishful thinking. It sends a message that
there is something essentially happy and carefree about the homosexual
lifestyle – which there is not.
f. Again, this “freedom” to disobey should be seen as God’s judgment,
not His kindness; those who engage in such acts are receiving in
themselves the penalty of their error.
@The MacArthur Bible Commentary
1:27 receiving in themselves the penalty. Here, the law of sowing and reaping (Gal. 6:7, 8) takes effect, as
Paul refers to the self-destructive nature of this sin, of which AIDS
is one frightening evidence.